It is supposed by the Duke of Argyll that this formation was accumulated in a shallow lake or marsh in the neighbourhood of a volcano, which emitted showers of ashes and streams of lava. The tufaceous envelope of the fossils may have fallen into the lake from the air as volcanic dust, or have been washed down into it as mud from the adjoining land. Even without the aid of organic remains we might have decided that the deposit was newer than the chalk, for chalk- flints containing cretaceous fossils were detected by the duke in the principal mass of volcanic ashes or tuff. (Quarterly Geological Journal 1851 page 90.)

The late Edward Forbes observed that some of the plants of this formation resembled those of Croatia, described by Unger, and his opinion has been confirmed by Professor Heer, who found that the conifer most prevalent was the Sequoia Langsdorfii (Figure 153), also Corylus grossedentata, a Lower Miocene species of Switzerland and of Menat in Auvergne. There is likewise a plane-tree, the leaves of which seem to agree with those of Platanus aceroides (Figure 141 Chapter 14), and a fern which is as yet peculiar to Mull, Filicites hebridica, Forbes.

These interesting discoveries in Mull led geologists to suspect that the basalt of Antrim, in Ireland, and of the celebrated Giant's Causeway, might be of the same age. The volcanic rocks that overlie the chalk, and some of the strata associated with and interstratified between masses of basalt, contain leaves of dicotyledonous plants, somewhat imperfect, but resembling the beech, oak, and plane, and also some coniferae of the genera pine and Sequoia. The general dearth of strata in the British Isles, intermediate in age between the formation of the Eocene and Pliocene periods, may arise, says Professor Forbes, from the extent of dry land which prevailed in that vast interval of time. If land predominated, the only monuments we are likely ever to find of Miocene date are those of lacustrine and volcanic origin, such as the Bovey Coal in Devonshire, the Ardtun beds in Mull, or the lignites and associated basalts in Antrim.

LOWER MIOCENE, UNITED STATES: NEBRASKA.

In the territory of Nebraska, on the Upper Missouri, near the Platte River, latitude 42 degrees N., a tertiary formation occurs, consisting of white limestone, marls, and siliceous clay, described by Dr. D. Dale Owen (David Dale Owen Geological Survey of Wisconsin etc. Philadelphia 1852.), in which many bones of extinct quadrupeds, and of chelonians of land or fresh-water forms, are met with. Among these, Dr. Leidy describes a gigantic quadruped, called by him Titanotherium, nearly allied to the Palaeotherium, but larger than any of the species found in the Paris gypsum. With these are several species of the genus Oreodon, Leidy, uniting the characters of pachyderms and ruminants also; Eucrotaphus, another new genus of the same mixed character; two species of rhinoceros of the sub-genus Acerotherium, a Lower Miocene form of Europe before mentioned; two species of Archaeotherium, a pachyderm allied to Chaeropotamus and Hyracotherium; also Paebrotherium, an extinct ruminant allied to Dorcatherium, Kaup; also Agriochoerus, of Leidy, a ruminant allied to Merycopotamus of Falconer and Cautley; and, lastly, a large carnivorous animal of the genus Machairodus, the most ancient example of which in Europe occurs in the Lower Miocene strata of Auvergne, but of which some species are found in Pliocene deposits. The turtles are referred to the genus Testudo, but have some affinity to Emys. On the whole, the Nebraska formation is probably newer than the Paris gypsum, and referable to the Lower Miocene period, as above defined.

CHAPTER XVI.

EOCENE FORMATIONS.

Eocene Areas of North of Europe. Table of English and French Eocene Strata. Upper Eocene of England. Bembridge Beds. Osborne or St. Helen's Beds. Headon Series. Fossils of the Barton Sands and Clays. Middle Eocene of England. Shells, Nummulites, Fish and Reptiles of the Bracklesham Beds and Bagshot Sands. Plants of Alum Bay and Bournemouth. Lower Eocene of England. London Clay Fossils. Woolwich and Reading Beds formerly called "Plastic Clay." Fluviatile Beds underlying Deep-sea Strata. Thanet Sands. Upper Eocene Strata of France. Gypseous Series of Montmartre and Extinct Quadrupeds. Fossil Footprints in Paris Gypsum. Imperfection of the Record. Calcaire Silicieux. Gres de Beauchamp. Calcaire Grossier. Miliolite Limestone. Soissonnais Sands. Lower Eocene of France. Nummulitic Formations of Europe, Africa, and Asia. Eocene Strata in the United States. Gigantic Cetacean.

EOCENE AREAS OF THE NORTH OF EUROPE.

(FIGURE 164. Map of the principal Eocene areas of North-western Europe, showing: Shaded dotted: Hypogene rocks and strata older than the Devonian. Shaded horizontal lines: Eocene formations. NB.— the space left blank is occupied by fossiliferous formations from the Devonian to the chalk inclusive.)

The strata next in order in the descending series are those which I term Eocene.

In the map in Figure 164, the position of several Eocene areas in the north of Europe is pointed out. When this map was constructed I classed as the newer part of the Eocene those Tertiary strata which have been described in the last chapter as Lower Miocene, and to which M. Beyrich has given the name of Oligocene. None of these occur in the London Basin, and they occupy in that of Hampshire, as we have seen in Chapter 15, too insignificant a superficial area to be noticed in a map on this scale. They fill a larger space in the Paris Basin between the Seine and the Loire, and constitute also part of the northern limits of the area of the Netherlands which are shaded in the map.

TABLE 16.1. TABLE OF ENGLISH AND FRENCH EOCENE STRATA.

COLUMN 1: NAME OF STRATA.

COLUMN 2: ENGLISH SUBDIVISIONS.

COLUMN 3: FRENCH EQUIVALENTS.

UPPER EOCENE.

A.1: Bembridge series, Isle of Wight: Gypseous series of Montmartre.

A.2: Osborne or St. Helen's series, Isle of Wight: Calcaire siliceux, or Travertin Inferieur.

A.3: Headon series, Isle of Wight: Calcaire siliceux, or Travertin Inferieur.

A.4: Barton series. Sands and clays of Barton Cliff, Hants: Gres de Beauchamp, or Sables Moyens.

MIDDLE EOCENE.

B.1: Bracklesham series: Calcaire Grossier.

B.2: Alum Bay and Bournemouth beds: Wanting in France?

B.2: Wanting in England?: Soissonnais Sands, or Lits Coquilliers.

LOWER EOCENE.

C.1: London Clay: Argile de Londres, Cassel, near Dunkirk.

C.2: Woolwich and Reading series: Argile plastique and lignite.

C.3: Thanet sands: Sables de Bracheux.

It is in the northern part of the Isle of Wight that we have the uppermost beds of the true Eocene best exhibited— namely, those which correspond in their fossils with the celebrated gypsum of the Paris basin before alluded to in Chapter 15 (see Table 16.1). That gypsum has been selected by almost all Continental geologists as affording the best line of demarkation between the Middle and Lower Tertiary, or, in other words, between the Lower Miocene and Eocene formations.

In reference to Table 16.1 I may observe, that the correlation of the French and English subdivisions here laid down is often a matter of great doubt and difficulty, notwithstanding their geographical proximity. This arises from various circumstances, partly from the former prevalence of marine conditions in one basin simultaneously with fluviatile or lacustrine in the other, and sometimes from the existence of land in one area causing a break or absence of all records during a period when deposits may have been in progress in the other basin. As bearing on this subject, it may be stated that we have unquestionable evidence of oscillations of level shown by the superposition of salt or brackish-water strata to fluviatile beds; and those of deep-sea origin to strata formed in shallow water. Even if the upward and downward movements were uniform in amount and direction, which is very improbable, their effect in producing the conversion of sea into land or land into sea would be different, according to the previous shape and varying elevation of the land and bottom of the sea. Lastly, denudation, marine and subaerial, has frequently caused the absence of deposits in one basin of corresponding age to those in the other, and this destructive agency has been more than ordinarily effective on account of the loose and unconsolidated nature of the sands and clays.

UPPER EOCENE OF ENGLAND.

BEMBRIDGE SERIES, A.1.

These beds are about 120 feet thick, and, as stated in Chapter 15, lie immediately under the Hempstead beds, near Yarmouth, in the Isle of Wight, being conformable with those Lower Miocene strata. They consist of marls, clays, and limestones of fresh-water, brackish, and marine origin. Some of the most abundant shells, as Cyrena semistriata var., and Paludina lenta, Figure 163 Chapter 15, are common to this and to the overlying Hempstead series; but the majority of the species are distinct. The following are the subdivisions described by the late Professor Forbes:

(FIGURE 165. Melania turritissima, Forbes. Bembridge.)

a. Upper marls, distinguished by the abundance of Melania turritissima, Forbes (Figure 165).

(FIGURE 166. Fragment of carapace of Trionyx. Bembridge Beds, Isle of Wight.)

b. Lower marls, characterised by Cerithium mutabile, Cyrena pulchra, etc., and by the remains of Trionyx (see Figure 166).

c. Green marls, often abounding in a peculiar species of oyster, and accompanied by Cerithium, Mytilus, Arca, nucula, etc.)

(FIGURE 167. Bulimus ellipticus, Sowerby. Bembridge Limestone. 1/2 natural size.)

(FIGURE 168. Helix occlusa, Edwards. Bembridge Limestone, Isle of Wight.)

(FIGURE 169. Paludina orbicularis. Bembridge.)

(FIGURE 170. Planorbis discus, Edwards. Bembridge. 1/2 diameter.)

(FIGURE 171. Lymnea longiscata, Brand. Natural size.)

(FIGURE 172. Chara tuberculata, seed-vessel. Bembridge Limestone, Isle of Wight.)

d. Bembridge limestones, compact cream-coloured limestones alternating with shales and marls, in all of which land-shells are common, especially at Sconce, near Yarmouth, as described by Mr. F. Edwards. The Bulimus ellipticus, Figure 167, and Helix occlusa, Figure 168, are among its best known land-shells. Paludina orbicularis, Figure 169, is also of frequent occurrence. One of the bands is filled with a little globular Paludina. Among the fresh-water pulmonifera, Lymnea longiscata (Figure 171) and Planorbis discus (Figure 170) are the most generally distributed: the latter represents or takes the place of the Planorbis euomphalus (see Figure 175) of the more ancient Headon series. Chara tuberculata (Figure 172) is the characteristic Bembridge gyrogonite or seed-vessel.

(FIGURE 173. Anoplotherium commune. Binstead, Isle of Wight. Lower molar tooth, natural size.)

(FIGURE 174. Palaeotherium magnum, Cuvier.)

(FIGURE 175. Planorbis euomphalus, Sowerby. Headon Hill. 1/2 diameter.)

From this formation on the shores of Whitecliff Bay, Dr. Mantell obtained a fine specimen of a fan palm, Flabellaria Lamanonis, Brong., a plant first obtained from beds of corresponding age in the suburbs of Paris. The well-known building- stone of Binstead, near Ryde, a limestone with numerous hollows caused by Cyrenae which have disappeared and left the moulds of their shells, belongs to this subdivision of the Bembridge series. In the same Binstead stone Mr. Pratt and the Reverend Darwin Fox first discovered the remains of mammalia characteristic of the gypseous series of Paris, as Palaeotherium magnum (Figure 174), Palaeotherium medium, Palaeotherium minus, Palaeotherium minimum, Palaeotherium curtum, Palaeotherium crassum; also Anoplotherium commune (Figure 173), Anoplotherium secundarium, Dichobune cervinum, and Chaeropotamus Cuvieri. The Palaeothere above alluded to resembled the living tapir in the form of the head, and in having a short proboscis, but its molar teeth were more like those of the rhinoceros. Palaeotherium magnum was of the size of a horse, three or four feet high. The woodcut, Figure 174, is one of the restorations which Cuvier attempted of the outline of the living animal, derived from the study of the entire skeleton. As the vertical range of particular species of quadrupeds, so far as our knowledge extends, is far more limited than that of the testacea, the occurrence of so many species at Binstead, agreeing with fossils of the Paris gypsum, strengthens the evidence derived from shells and plants of the synchronism of the two formations.

OSBORNE OR ST. HELEN'S SERIES, A.2.

This group is of fresh and brackish-water origin, and very variable in mineral character and thickness. Near Ryde, it supplies a freestone much used for building, and called by Professor Forbes the Nettlestone grit. In one part ripple-marked flagstones occur, and rocks with fucoidal markings. The Osborne beds are distinguished by peculiar species of Paludina, Melania, and Melanopsis, as also of Cypris and the seeds of Chara.

HEADON SERIES A.3.

These beds are seen both in Whitecliff Bay, Headon Hill, and Alum Bay, or at the east and west extremities of the Isle of Wight. The upper and lower portions are fresh-water, and the middle of mixed origin, sometimes brackish and marine. Everywhere Planorbis euomphalus, Figure 175, characterises the fresh-water deposits, just as the allied form, Planorbis discus, Figure 170, does the Bembridge limestone. The brackish-water beds contain Potamomya plana, Cerithium mutabile, and Potamides cinctus (Figure 37 Chapter 3), and the marine beds Venus (or Cytherea) incrassata, a species common to the Limburg beds and Gres de Fontainebleau, or the Lower Miocene series. The prevalence of salt-water remains is most conspicuous in some of the central parts of the formation.

(FIGURE 176. Helix labyrinthica, Say. Headon Hill, Isle of Wight; and Hordwell Cliff, Hants— also recent.)

(FIGURE 177. Neritina concava, Sowerby. Headon series.)

(FIGURE 178. Lymnea caudata, Edw. Headon series.)

(FIGURE 179. Cerithium concavum, Sowerby. Headon series.)

Among the shells which are widely distributed through the Headon series are Neritina concava (Figure 177), Lymnea caudata (Figure 178), and Cerithium concavum (Figure 179). Helix labyrinthica, Say (Figure 176), a land-shell now inhabiting the United States, was discovered in this series by Mr. Searles Wood in Hordwell Cliff. It is also met with in Headon Hill, in the same beds. At Sconce, in the Isle of Wight, it occurs in the Bembridge series, and affords a rare example of an Eocene fossil of a species still living, though, as usual in such cases, having no local connection with the actual geographical range of the species. The lower and middle portion of the Headon series is also met with in Hordwell Cliff (or Hordle, as it is often spelt), near Lymington, Hants. Among the shells which abound in this cliff are Paludina lenta and various species of Lymnea, Planorbis, Melania, Cyclas, Unio, Potamomya, Dreissena, etc.

Among the chelonians we find a species of Emys, and no less than six species of Trionyx; among the saurians an alligator and a crocodile; among the ophidians two species of land-snakes (Paleryx, Owen); and among the fish Sir P. Egerton and Mr. Wood have found the jaws, teeth, and hard shining scales of the genus Lepidosteus, or bony pike of the American rivers. This same genus of fresh-water ganoids has also been met with in the Hempstead beds in the Isle of Wight. The bones of several birds have been obtained from Hordwell, and the remains of quadrupeds of the genera Palaeotherium (Palaeotherium minus), Anoplotherium, Anthracotherium, Dichodon, Dichobune, Spalacodon, and Hyaenodon. The latter offers, I believe, the oldest known example of a true carnivorous animal in the series of British fossils, although I attach very little theoretical importance to the fact, because herbivorous species are those most easily met with in a fossil state in all save cavern deposits. In another point of view, however, this fauna deserves notice. Its geological position is considerably lower than that of the Bembridge or Montmartre beds, from which it differs almost as much in species as it does from the still more ancient fauna of the Lower Eocene beds to be mentioned in the sequel. It therefore teaches us what a grand succession of distinct assemblages of mammalia flourished on the earth during the Eocene period.

Many of the marine shells of the brackish-water beds of the above series, both in the Isle of Wight and Hordwell Cliff, are common to the underlying Barton Clay: and, on the other hand, there are some fresh-water shells, such as Cyrena obovata, which are common to the Bembridge beds, notwithstanding the intervention of the St. Helen's series. The white and green marls of the Headon series, and some of the accompanying limestones, often resemble the Eocene strata of France in mineral character and colour in so striking a manner as to suggest the idea that the sediment was derived from the same region or produced contemporaneously under very similar geographical circumstances.

(FIGURE 180. Solenastraea cellulosa, Duncan. Brockenhurst.)

At Brockenhurst, near Lyndhurst, in the New Forest, marine strata have recently been found containing fifty-nine shells, of which many have been described by Mr. Edwards. These beds rest on the Lower Headon, and are considered as the equivalent of the middle part of the Headon series, many of the shells being common to the brackish-water or Middle Headon beds of Colwell and Whitecliff Bays, such as Cancellaria muricata, Sowerby, Fusus labiatus, Sowerby, etc. In these beds at Brockenhurst, corals, ably described by Dr. Duncan, have recently been found in abundance and perfection; see Figure 180, Solenastraea cellulosa.

Baron von Konen has pointed out that no less than forty-six out of the fifty- nine Brockenhurst shells, or a proportion of 78 per cent, agree with species occurring in Dumont's Lower Tongrian formation in Belgium. (Quarterly Geological Journal volume 20 page 97 1864.) This being the case, we might fairly expect that if we had a marine equivalent of the Bembridge series or of the contemporaneous Paris gypsum, we should find it to contain a still greater number of shells common to the Tongrian beds of Belgium, but the exact correlation of these fresh-water groups of France, Belgium, and Britain has not yet been fully made out. It is possible that the Tongrian of Dumont may be newer than the Bembridge series, and therefore referable to the Lower Miocene. If ever the whole series should be complete, we must be prepared to find the marine equivalent of the Bembridge beds, or the uppermost Eocene, passing by imperceptible shades into the inferior beds of the overlying Miocene strata.

Among the fossils found in the Middle Headon are Cytherea incrassata and Cerithium plicatum (Figure 160 Chapter 15). These shells, especially the latter, are very characteristic of the Lower Miocene, and their occurrence in the Headon series has been cited as an objection to the line proposed to be drawn between Miocene and Eocene. But if we were to attach importance to such occasional passages, we should soon find that no lines of division could be drawn anywhere, for in the present state of our knowledge of the Tertiary series there will always be species common to beds above and below our boundary-lines.

BARTON SERIES (SANDS AND CLAYS), A.4 TABLE 16.1.)

(FIGURE 181. Chama squamosa, Eichw. Barton.)

Both in the Isle of Wight, and in Hordwell Cliff, Hants, the Headon beds, above- mentioned, rest on white sands usually devoid of fossils, and used in the Isle of Wight for making glass. In one of these sands Dr. Wright found Chama squamosa, a Barton Clay shell, in great plenty, and certain impressions of marine shells have been found in sands supposed to be of the same age in Whitecliff Bay. These sands have been called Upper Bagshot in the maps of our Government Survey, but this identification of a fossiliferous series in the Isle of Wight with an unfossiliferous formation in the London Basin can scarcely be depended upon. The Barton Clay, which immediately underlies these sands, is seen vertical in Alum Bay, Isle of Wight, and nearly horizontal in the cliffs of the mainland near Lymington. This clay, together with the Bracklesham beds, presently to be described, has been termed Middle Bagshot by the Survey. In Barton Cliff, where it attains a thickness of about 300 feet, it is rich in marine fossils.

It was formerly confounded with the London Clay, an older Eocene deposit of very similar mineral character, to be mentioned below, which contains many shells in common, but not more than one-fourth of the whole. In other words, there are known at present 247 species in the London Clay and 321 in that of Barton, and only 70 common to the two formations. Fifty-six of these have been found in the intermediate Bracklesham beds, and the reappearance of the other 14 may imply a return of similar conditions, whether of temperature or depth or of a muddy argillaceous bottom, common to the two periods of the London and Barton Clays. According to M. Hebert, the most characteristic Barton Clay fossils correspond to those of the Gres de Beauchamp, or Sables Moyens, of the Paris Basin, but it also contains many common to the older Calcaire Grossier.

SHELLS OF THE BARTON CLAY.

(FIGURE 182. Mitra scabra, Sowerby.)

(FIGURE 183. Voluta ambigua, Sol.)

(FIGURE 184. Typhis pungens, Brand.)

(FIGURE 185. Voluta athleta, Sol. Barton and Bracklesham.)

(FIGURE 186. Terebellum fusiforme, Lam. Barton and Bracklesham.)

(FIGURE 187. Terebellum sopita, Brand.)

(FIGURE 188. Cardita sulcata, Brand. Barton.)

(FIGURE 189. Crassatella sulcata, Sowerby. Bracklesham and Barton.)

(FIGURE 190. Nummulites variolaria, Lam. Var. of Nummulites radiata, Sowerby. Middle Eocene, Bracklesham Bay. a. Natural size. b. Magnified.)

Certain foraminifera called Nummulites begin, when we study the Tertiary formations in a descending order, to make their first appearance in these beds. A small species called Nummulites variolaria, Figure 190, is found both on the Hampshire coast and in beds of the same age in Whitecliff Bay, in the Isle of Wight. Several marine shells, such as Corbula pisum (Figure 158), are common to the Barton beds and the Hempstead or Lower Miocene series, and a still greater number, as before stated, are common to the Headon series.

MIDDLE EOCENE, ENGLAND.

BRACKLESHAM BEDS AND BAGSHOT SANDS (B.1, TABLE 16.1).

(FIGURE 191. Cardita (Venericardia) planicosta, Lam.)

(FIGURE 192. Nummulites (Nummularia) laevigata. Bracklesham. Dixon's Fossils of Sussex, Plate 8. a. Section of nummulite. b. Group, with an individual showing the exterior of the shell.)

Beneath the Barton Clay we find in the north of the Isle of Wight, both in Alum and Whitecliff Bays, a great series of various coloured sands and clays for the most part unfossiliferous, and probably of estuarine origin. As some of these beds contain Cardita planicosta (Figure 191) they have been identified with the marine beds much richer in fossils seen in the coast section in Bracklesham Bay near Chichester in Sussex, where the strata consist chiefly of green clayey sands with some lignite. Among the Bracklesham fossils besides the Cardita, the huge Cerithium giganteum is seen, so conspicuous in the Calcaire Grossier of Paris, where it is sometimes two feet in length. The Nummulites laevigata (see Figure 192), so characteristic of the lower beds of the Calcaire Grossier in France, where it sometimes forms stony layers, as near Compiegne, is very common in these beds, together with Nummulites scabra and Nummulites variolaria. Out of 193 species of testacea procured from the Bagshot and Bracklesham beds in England, 126 occur in the Calcaire Grossier in France. It was clearly, therefore, coeval with that part of the Parisian series more nearly than with any other.

(FIGURE 193. Palaeophis typhoeus, Owen; an Eocene sea-serpent. Bracklesham. a, b. Vertebra, with long neural spine preserved. c. Two vertebrae articulated together.)

(FIGURE 194. Defensive spine of Ostracion. Bracklesham.)

(FIGURE 195. Dental plates of Myliobates Edwardsi. Bracklesham Bay. Dixon's Fossils of Sussex, Plate 8.)

According to tables compiled from the best authorities by Mr. Etheridge, the number of mollusca now known from the Bracklesham beds in Great Britain is 393, of which no less than 240 are peculiar to this subdivision of the British Eocene series, while 70 are common to the Older London Clay, and 140 to the Newer Barton Clay. The volutes and cowries of this formation, as well as the lunulites and corals, favour the idea of a warm climate having prevailed, which is borne out by the discovery of a serpent, Palaeophis typhoeus (see Figure 193), exceeding, according to Professor Owen, twenty feet in length, and allied in its osteology to the Boa, Python, Coluber, and Hydrus. The compressed form and diminutive size of certain caudal vertebrae indicate so much analogy with Hydrus as to induce Professor Owen to pronounce this extinct ophidian to have been marine. (Palaeontological Society Monograph Reptiles part 2 page 61.) Among the companions of the sea-snake of Bracklesham was an extinct crocodile (Gavialis Dixoni, Owen), and numerous fish, such as now frequent the seas of warm latitudes, as the Ostracion of the family Balistidae, of which a dorsal spine is figured (see Figure 194), and gigantic rays of the genus Myliobates (see Figure 195).

(FIGURE 196. Carcharodon angustidens, Agassiz.)

(FIGURE 197. Otodus obliquus, Agassiz.)

(FIGURE 198. Lamna elegans, Agassiz.)

(FIGURE 199. Galeocerdo latidens, Agassiz.)

The teeth of sharks also, of the genera Carcharodon, Otodus, Lamna, Galeocerdo, and others, are abundant. (See Figures 196, 197, 198, 199.)

MARINE SHELLS OF BRACKLESHAM BEDS.

ALUM BAY AND BOURNEMOUTH BEDS. (LOWER BAGSHOT OF ENGLISH SURVEY), B.2, TABLE 16.1.)

(FIGURE 200. Pleurotoma attenuata, Sowerby.)

(FIGURE 201. Voluta Selseiensis, Edwards.)

(FIGURE 202. Turritella multisulcata, Lam.)

(FIGURE 203. Lucina serrata, Sowerby. Magnified.)

(FIGURE 204. Conus deperditus, Brug.)

To that great series of sands and clays which intervene between the equivalents of the Bracklesham Beds and the London Clay or Lower Eocene, our Government Survey has given the name of the Lower Bagshot sands, for they are supposed to agree in age with the inferior unfossiliferous sands of the country round Bagshot in the London Basin. This part of the series is finely exposed in the vertical beds of Alum bay, in the Isle of Wight, and east and west of Bournemouth, on the south coast of Hampshire. In some of the close and white compact clays of this locality, there are not only dicotyledonous leaves, but numerous fronds of ferns allied to Gleichenia which are well preserved with their fruit.

None of the beds are of great horizontal extent, and there is much cross- stratification in the sands, and in some places black carbonaceous seams and lignite. In the midst of these leaf-beds in Studland Bay, Purbeck shells of the genus Unio attest the fresh-water origin of the white clay.

No less than forty species of plants are mentioned by MM. de la Harpe and Gaudin from this formation in Hampshire, among which the Proteaceae (Dryandra, etc.) and the fig tribe are abundant, as well as the cinnamon and several other laurineae, with some papilionaceous plants. On the whole, they remind the botanist of the types of subtropical India and Australia. (Heer Climat et Vegetation du Pays Tertiaire page 172.)

Heer has mentioned several species which are common to this Alum Bay flora and that of Monte Bolca, near Verona, so celebrated for its fossil fish, and where the strata contain nummulites and other Middle Eocene fossils. He has particularly alluded to Aralia primigenia (of which genus a fruit has since been found by Mr. Mitchell at Bournemouth), Daphnogene Veronensis, and Ficus granadilla, as among the species common to and characteristic of the Isle of Wight and Italian Eocene beds; and he observes that in the flora of this period these forms of a temperate climate which constitute a marked feature in the European Miocene formations, such as the willow, poplar, birch, alder, elm, hornbeam, oak, fir, and pine, are wanting. The American types are also absent, or much more feebly represented than in the Miocene period, although fine specimens of the fan-palm (Sabal) have been found in these Eocene clays at Studland. The number of exotic forms which are common to the Eocene and Miocene strata of Europe, like those to be alluded to in the sequel which are common to the Eocene and Cretaceous fauna, demonstrate the remoteness of the times in which the geographical distribution of living plants originated. A great majority of the Eocene genera have disappeared from our temperate climates, but not the whole of them; and they must all have exerted some influence on the assemblages of species which succeeded them. Many of these last occurring in the Upper Miocene are indeed so closely allied to the flora now surviving as to make it questionable, even in the opinion of naturalists opposed to the doctrine of transmutation, whether they are not genealogically related the one to the other.

LOWER EOCENE FORMATIONS, ENGLAND.

LONDON CLAY (C.1, TABLE 16.1).

This formation underlies the preceding, and sometimes attains a thickness of 500 feet. It consists of tenacious brown and bluish-grey clay, with layers of concretions called septaria, which abound chiefly in the brown clay, and are obtained in sufficient numbers from sea-cliffs near Harwich, and from shoals off the coast of Essex and the Isle of Sheppey, to be used for making Roman cement. The total number of British fossil mollusca known at present (January, 1870) in this formation are 254, of which 166 are peculiar, or not found in other Eocene beds in this country. The principal localities of fossils in the London clay are Highgate Hill, near London, the Island of Sheppey at the mouth of the Thames, and Bognor on the Sussex coast. Out of 133 fossil shells, Mr. Prestwich found only 20 to be common to the Calcaire Grossier (from which 600 species have been obtained), while 33 are common to the "Lits Coquilliers" (see below), in which 200 species are known in France.

In the Island of Sheppey near the mouth of the Thames, the thickness of the London Clay is estimated by Mr. Prestwich to be more than 500 feet, and it is in the uppermost 50 feet that a great number of fossil fruits were obtained, being chiefly found on the beach when the sea has washed away the clay of the rapidly wasting cliffs.

(FIGURE 205. Nipadites ellipticus, Bowerbank. Fossil fruit of palm, from Sheppey.)

Mr. Bowerbank, in a valuable publication on these fossil fruits and seeds, has described no less than thirteen fruits of palms of the recent type Nipa, now only found in the Molucca and Philippine Islands, and in Bengal (see Figure 205). In the delta of the Ganges, Dr. Hooker observed the large nuts of Nipa fruticans floating in such numbers in the various arms of that great river, as to obstruct the paddle-wheels of steamboats. These plants are allied to the cocoanut tribe on the one side, and on the other to the Pandanus, or screw-pine. There are also met with three species of Anona, or custard-apple; and cucurbitaceous fruits (of the gourd and melon family), and fruits of various species of Acacia.

Besides fir-cones or fruit of true Coniferae there are cones of Proteaceae in abundance, and the celebrated botanist the late Robert Brown pointed out the affinity of these to the New Holland types Petrophila and Isopogon. Of the first there are about fifty, and of the second thirty described species now living in Australia.

(FIGURE 206. Eocene Proteaceous Fruit. Petrophiloides Richardsoni. London Clay, Sheppey. Natural size. a. Cone. b. Section of cone showing the position of the seeds.)

Ettingshausen remarked in 1851 that five of the fossil species from Sheppey, named by Bowerbank (Fossil Fruits and Seeds of London Clay Plates 9 and 10.) were specimens of the same fruit (see Figure 206), in different states of preservation; and Mr. Carruthers, having examined the original specimens now in the British Museum, tells me that all these cones from Sheppey may be reduced to two species, which have an undoubted affinity to the two existing Australian genera above mentioned, although their perfect identity in structure can not be made out.

The contiguity of land may be inferred not only from these vegetable productions, but also from the teeth and bones of crocodiles and turtles, since these creatures, as Dean Conybeare remarked, must have resorted to some shore to lay their eggs. Of turtles there were numerous species referred to extinct genera. These are, for the most part, not equal in size to the largest living tropical turtles. A sea-snake, which must have been thirteen feet long, of the genus Palaeophis before mentioned, has also been described by Professor Owen from Sheppey, of a different species from that of Bracklesham, and called Palaeophis toliapicus. A true crocodile, also, Crocodilus toliapicus, and another saurian more nearly allied to the gavial, accompany the above fossils; also the relics of several birds and quadrupeds. One of these last belongs to the new genus Hyracotherium of Owen, of the hog tribe, allied to Chaeropotamus, another is a Lophiodon; a third a pachyderm called Coryphodon eocaenus by Owen, larger than any existing tapir. All these animals seem to have inhabited the banks of the great river which floated down the Sheppey fruits. They imply the existence of a mammiferous fauna antecedent to the period when nummulites flourished in Europe and Asia, and therefore before the Alps, Pyrenees, and other mountain-chains now forming the backbones of great continents, were raised from the deep; nay, even before a part of the constituent rocky masses now entering into the central ridges of these chains had been deposited in the sea.

SHELLS OF THE LONDON CLAY.

(FIGURE 207. Voluta nodosa, Sowerby. Highgate.)

(FIGURE 208. Phorus extensus, Sowerby. Highgate.)

(FIGURE 209. Rostellaria (Hippocrenes) ampla, Brander. 1/3 of natural size; also found in the Barton clay.)

(FIGURE 210. Nautilus centralis, Sowerby. Highgate.)

(FIGURE 211. Aturia ziczac, Bronn. Syn. Nautilus ziczac, Sowerby. London clay. Sheppey.)

(FIGURE 212. Belosepia sepioidea, De Blainv. London clay. Sheppey.)

(FIGURE 213. Leda amygdaloides, Sowerby. Highgate.)

(FIGURE 214. Cyptodon (Axinus) angulatum, Sowerby. London clay. Hornsey.)

(FIGURE 215. Astropecten crispatus, E. Forbes. Sheppey.)

The marine shells of the London Clay confirm the inference derivable from the plants and reptiles in favour of a high temperature. Thus many species of Conus and Voluta occur, a large Cypraea, C. oviformis, a very large Rostellaria (Figure 209), a species of Cancellaria, six species of Nautilus (Figure 211), besides other Cephalopoda of extinct genera, one of the most remarkable of which is the Belosepia (Figure 212). Among many characteristic bivalve shells are Leda amygdaloides (Figure 213) and Cryptodon angulatum (Figure 214), and among the Radiata a star-fish, Astropecten (Figure 215.)

These fossils are accompanied by a sword-fish (Tetrapterus priscus, Agassiz), about eight feet long, and a saw-fish (Pristis bisulcatus, Agassiz), about ten feet in length; genera now foreign to the British seas. On the whole, about eighty species of fish have been described by M. Agassiz from these beds of Sheppey, and they indicate, in his opinion, a warm climate.

In the lower part of the London clay at Kyson, a few miles east of Woodbridge, the remains of mammalia have been detected. Some of these have been referred by Professor Owen to an opossum, and others to the genus Hyracotherium. The teeth of this last-mentioned pachyderm were at first, in 1840, supposed to belong to a monkey, an opinion afterwards abandoned by Owen when more ample materials for comparison were obtained.

WOOLWICH AND READING SERIES (C.2, TABLE 16.1.)

This formation was formerly called the Plastic Clay, as it agrees with a similar clay used in pottery which occupies the same position in the French series, and it has been used for the like purposes in England. (Prestwich Quarterly Geological Journal volume 10.)

No formations can be more dissimilar, on the whole, in mineral character than the Eocene deposits of England and Paris; those of our own island being almost exclusively of mechanical origin— accumulations of mud, sand, and pebbles; while in the neighbourhood of Paris we find a great succession of strata composed of limestones, some of them siliceous, and of crystalline gypsum and siliceous sandstone, and sometimes of pure flint used for millstones. Hence it is often impossible, as before stated, to institute an exact comparison between the various members of the English and French series, and to settle their respective ages. But in regard to the division which we have now under consideration, whether we study it in the basins of London, Hampshire, or Paris, we recognise as a general rule the same mineral character, the beds consisting over a large area of mottled clays and sand, with lignite, and with some strata of well-rolled flint pebbles, derived from the chalk, varying in size, but occasionally several inches in diameter. These strata may be seen in the Isle of Wight in contact with the chalk, or in the London basin, at Reading, Blackheath, and Woolwich. In some of the lowest of them, banks of oysters are observed, consisting of Ostrea bellovacina, so common in France in the same relative position. In these beds at Bromley, Dr. Buckland found a large pebble to which five full-grown oysters were affixed, in such a manner as to show that they had commenced their first growth upon it, and remained attached to it through life.

(FIGURE 216. Cyrena cuneiformis, Sowerby. Natural size. Woolwich clays.)

(FIGURE 217. Melania (Melanatria) inquinata, Des. Syn. Cerithium melanoides, Sowerby. Woolwich clays.)

In several places, as at Woolwich on the Thames, at Newhaven in Sussex, and elsewhere, a mixture of marine and fresh-water testacea distinguishes this member of the series. Among the latter, Cyrena cuneiformis (see Figure 216) and Melania inquinata (see Figure 217) are very common, as in beds of corresponding age in France. They clearly indicate points where rivers entered the Eocene sea. Usually there is a mixture of brackish, fresh-water, and marine shells, and sometimes, as at Woolwich, proofs of the river and the sea having successively prevailed on the same spot. At New Charlton, in the suburbs of Woolwich, Mr. de la Condamine discovered in 1849, and pointed out to me, a layer of sand associated with well-rounded flint pebbles in which numerous individuals of the Cyrena tellinella were seen standing endwise with both their valves united, the siphonal extremity of each shell being uppermost, as would happen if the mollusks had died in their natural position. I have described a bank of sandy mud, in the delta of the Alabama River at Mobile, on the borders of the Gulf of Mexico, where in 1846 I dug out at low tide specimens of living species of Cyrena and of a Gnathodon, which were similarly placed with their shells erect, or in a posture which enables the animal to protrude its siphon upward, and draw in or reject water at pleasure. (Second Visit to the United States volume 2 page 104.) The water at Mobile is usually fresh, but sometimes brackish. At Woolwich a body of river-water must have flowed permanently into the sea where the Cyrenae lived, and they may have been killed suddenly by an influx of pure salt- water, which invaded the spot when the river was low, or when a subsidence of land took place. Traced in one direction, or eastward towards Herne Bay, the Woolwich beds assume more and more of a marine character; while in an opposite, or south-western direction, they become, as near Chelsea and other places, more fresh-water, and contain Unio, Paludina, and layers of lignite, so that the land drained by the ancient river seems clearly to have been to the south-west of the present site of the metropolis.

FLUVIATILE BEDS UNDERLYING DEEP-SEA STRATA.

Before the minds of geologists had become familiar with the theory of the gradual sinking of land, and its conversion into sea at different periods, and the consequent change from shallow to deep water, the fluviatile and littoral character of this inferior group appeared strange and anomalous. After passing through hundreds of feet of London clay, proved by its fossils to have been deposited in deep salt-water, we arrive at beds of fluviatile origin, and associated with them masses of shingle, attaining at Blackheath, near London, a thickness of 50 feet. These shingle banks are probably of marine origin, but they indicate the proximity of land, and the existence of a shore where the flints of the chalk were rolled into sand and pebbles, and spread over a wide space. We have, therefore, first, as before stated, evidence of oscillations of level during the accumulation of the Woolwich series, then of a great submergence, which allowed a marine deposit 500 thick to be laid over the antecedent beds of fresh and brackish water origin.

THANET SANDS (C.3 TABLE 16.1).

The Woolwich or plastic clay above described may often be seen in the Hampshire basin in actual contact with the chalk, constituting in such places the lowest member of the British Eocene series. But at other points another formation of marine origin, characterised by a somewhat different assemblage of organic remains, has been shown by Mr. Prestwich to intervene between the chalk and the Woolwich series. For these beds he has proposed the name of "Thanet Sands," because they are well seen in the Isle of Thanet, in the northern part of Kent, and on the sea-coast between Herne Bay and the Reculvers, where they consist of sands with a few concretionary masses of sandstone, and contain, among other fossils, Pholadomya cuneata, Cyprina morrisii, Corbula longirostris, Scalaria Bowerbankii, etc. The greatest thickness of these beds is 90 feet.

UPPER EOCENE FORMATIONS OF FRANCE.

The tertiary formations in the neighbourhood of Paris consist of a series of marine and fresh-water strata, alternating with each other, and filling up a depression in the chalk. The area which they occupy has been called the Paris Basin, and is about 180 miles in its greatest length from north to south, and about 90 miles in breadth from east to west. MM. Cuvier and Brongniart attempted, in 1810, to distinguish five different groups, comprising three fresh-water and two marine, which were supposed to imply that the waters of the ocean, and of rivers and lakes, had been by turns admitted into and excluded from the same area. Investigations since made in the Hampshire and London basins have rather tended to confirm these views, at least so far as to show that since the commencement of the Eocene period there have been great movements of the bed of the sea, and of the adjoining lands, and that the superposition of deep-sea to shallow-water deposits (the London Clay, for example, to the Woolwich beds) can only be explained by referring to such movements. It appears, notwithstanding, from the researches of M. Constant Prevost, that some of the minor alternations and intermixtures of fresh-water and marine deposits, in the Paris basin, may be accounted for without such changes of level, by imagining both to have been simultaneously in progress, in the same bay of the same sea, or a gulf into which many rivers entered.

GYPSEOUS SERIES OF MONTMARTRE (A.1, TABLE 16.1).

To enlarge on the numerous subdivisions of the Parisian strata would lead me beyond my present limits; I shall therefore give some examples only of the most important formations. Beneath the Gres de Fontainebleau, belonging to the Lower Miocene period, as before stated, we find, in the neighbourhood of Paris, a series of white and green marls, with subordinate beds of gypsum. These are most largely developed in the central parts of the Paris basin, and, among other places, in the hill of Montmartre, where its fossils were first studied by Cuvier.

The gypsum quarried there for the manufacture of plaster of Paris occurs as a granular crystalline rock, and, together with the associated marls, contains land and fluviatile shells, together with the bones and skeletons of birds and quadrupeds. Several land-plants are also met with, among which are fine specimens of the fan-palm or palmetto tribe (Flabellaria). The remains also of fresh-water fish, and of crocodiles and other reptiles, occur in the gypsum. The skeletons of mammalia are usually isolated, often entire, the most delicate extremities being preserved; as if the carcasses, clothed with their flesh and skin, had been floated down soon after death, and while they were still swollen by the gases generated by their first decomposition. The few accompanying shells are of those light kinds which frequently float on the surface of rivers, together with wood.

In this formation the relics of about fifty species of quadrupeds, including the genera Palaeotherium (see Figure 174), Anoplotherium (see Figure 218), and others, have been found, all extinct, and nearly four-fifths of them belonging to the Perissodactyle or odd-toed division of the order Pachydermata, which now contains only four living genera, namely, rhinoceros, tapir, horse, and hyrax. With them a few carnivorous animals are associated, among which are the Hyaenodon dasyuroides, a species of dog, Canis Parisiensis, and a weasel, Cynodon Parisiensis. Of the Rodentia are found a squirrel; of the Cheiroptera, a bat; while the Marsupalia (an order now confined to America, Australia, and some contiguous islands) are represented by an opossum.

Of birds, about ten species have been ascertained, the skeletons of some of which are entire. None of them are referable to existing species. (Cuvier, Oss. Foss. tome 3 page 255.) The same remark, according to MM. Cuvier and Agassiz, applies both to the reptiles and fish. Among the last are crocodiles and tortoises of the genera Emys and Trionyx.

(FIGURE 218. Xiphodon gracile, or Anoplotherium gracile, Cuvier. Restored outline.)

The tribe of land quadrupeds most abundant in this formation is such as now inhabits alluvial plains and marshes, and the banks of rivers and lakes, a class most exposed to suffer by river inundations. Among these were several species of Palaeotherium, a genus before alluded to. These were associated with the Anoplotherium, a tribe intermediate between pachyderms and ruminants. One of the three divisions of this family was called by Cuvier Xiphodon. Their forms were slender and elegant, and one, named Xiphodon gracile (Figure 218), was about the size of the chamois; and Cuvier inferred from the skeleton that it was as light, graceful, and agile as the gazelle.

FOSSIL FOOTPRINTS.

There are three superimposed masses of gypsum in the neighbourhood of Paris, separated by intervening deposits of laminated marl. In the uppermost of the three, in the valley of Montmorency, M. Desnoyers discovered in 1859 many footprints of animals occurring at no less than six different levels. (Sur des Empreintes de Pas d'Animaux par M. J. Desnoyers. Compte rendu de l'Institut 1859.) The gypsum to which they belong varies from thirty to fifty feet in thickness, and is that which has yielded to the naturalist the largest number of bones and skeletons of mammalia, birds, and reptiles. I visited the quarries, soon after the discovery was made known, with M. Desnoyers, who also showed me large slabs in the Museum at Paris, where, on the upper planes of stratification, the indented foot-marks were seen, while corresponding casts in relief appeared on the lower surfaces of the strata of gypsum which were immediately superimposed. A thin film of marl, which before it was dried and condensed by pressure must have represented a much thicker layer of soft mud, intervened between the beds of solid gypsum. On this mud the animals had trodden, and made impressions which had penetrated to the gypseous mass below, then evidently unconsolidated. Tracks of the Anoplotherium with its bisulcate hoof, and the trilobed footprints of Palaeotherium, were seen of different sizes, corresponding to those of several species of these genera which Cuvier had reconstructed, while in the same beds were foot-marks of carnivorous mammalia. The tracks also of fluviatile, lacustrine, and terrestrial tortoises (Emys, Trionyx, etc.) were discovered, also those of crocodiles, iguanas, geckos, and great batrachians, and the footprints of a huge bird, apparently a wader, of the size of the gastornis, to be mentioned in the sequel. There were likewise the impressions of the feet of other creatures, some of them clearly distinguishable from any of the fifty extinct types of mammalia of which the bones have been found in the Paris gypsum. The whole assemblage, says Desnoyers, indicate the shores of a lake, or several small lakes communicating with each other, on the borders of which many species of pachyderms wandered, and beasts of prey which occasionally devoured them. The tooth-marks of these last had been detected by palaeontologists long before on the bones and skulls of Paleotheres entombed in the gypsum.

IMPERFECTION OF THE RECORD.

These foot-marks have revealed to us new and unexpected proofs that the air- breathing fauna of the Upper Eocene period in Europe far surpassed in the number and variety of its species the largest estimate which had previously been formed of it. We may now feel sure that the mammalia, reptiles, and birds which have left portions of their skeletons as memorials of their existence in the solid gypsum constituted but a part of the then living creation. Similar inferences may be drawn from the study of the whole succession of geological records. In each district the monuments of periods embracing thousands, and probably in some instances hundreds of thousands of years, are totally wanting. Even in the volumes which are extant the greater number of the pages are missing in any given region, and where they are found they contain but few and casual entries of the physical events or living beings of the times to which they relate. It may also be remarked that the subordinate formations met with in two neighbouring countries, such as France and England (the minor Tertiary groups above enumerated), commonly classed as equivalents and referred to corresponding periods, may nevertheless have been by no means strictly coincident in date. Though called contemporaneous, it is probable that they were often separated by intervals of many thousands of years. We may compare them to double stars, which appear single to the naked eye because seen from a vast distance in space, and which really belong to one and the same stellar system, though occupying places in space extremely remote if estimated by our ordinary standard of terrestrial measurements.

CALCAIRE SILICIEUX, OR TRAVERTIN INFERIEUR (A.2 AND 3 TABLE 16.1).

This compact siliceous limestone extends over a wide area. It resembles a precipitate from the waters of mineral springs, and is often traversed by small empty sinuous cavities. It is, for the most part, devoid of organic remains, but in some places contains fresh-water and land species, and never any marine fossils. The calcaire siliceux and the calcaire grossier usually occupy distinct parts of the Paris basin, the one attaining its fullest development in those places where the other is of slight thickness. They are described by some writers as alternating with each other towards the centre of the basin, as at Sergy and Osny.

The gypsum, with its associated marls before described, is in greatest force towards the centre of the basin, where the calcaire grossier and calcaire silicieux are less fully developed.

GRES DE BEAUCHAMP, OR SABLES MOYENS (A.4 TABLE 16.1).

In some parts of the Paris basin, sands and marls, called the Gres de Beauchamp, or Sables moyens, divide the gypseous beds from the calcaire grossier proper. These sands, in which a small nummulite (N. variolaria) is very abundant, contain more than 300 species of marine shells, many of them peculiar, but others common to the next division.

MIDDLE EOCENE FORMATIONS OF FRANCE.

CALCAIRE GROSSIER, UPPER AND MIDDLE (B.1 TABLE 16.1).

The upper division of this group consists in great part of beds of compact, fragile limestone, with some intercalated green marls. The shells in some parts are a mixture of Cerithium, Cyclostoma, and Corbula; in others Limnea, Cerithium, Paludina, etc. In the latter, the bones of reptiles and mammalia, Palaeotherium and Lophiodon, have been found. The middle division, or calcaire grossier proper, consists of a coarse limestone, often passing into sand. It contains the greater number of the fossil shells which characterise the Paris basin. No less than 400 distinct species have been procured from a single spot near Grignon, where they are imbedded in a calcareous sand, chiefly formed of comminuted shells, in which, nevertheless, individuals in a perfect state of preservation, both of marine, terrestrial, and fresh-water species, are mingled together. Some of the marine shells may have lived on the spot; but the Cyclostoma and Limnea, being land and fresh-water shells, must have been brought thither by rivers and currents, and the quantity of triturated shells implies considerable movement in the waters.

Nothing is more striking in this assemblage of fossil testacea than the great proportion of species referable to the genus Cerithium (Figures 160 and 161 Chapter 15). There occur no less than 137 species of this genus in the Paris basin, and almost all of them in the calcaire grossier. Most of the living Cerithia inhabit the sea near the mouths of rivers, where the waters are brackish; so that their abundance in the marine strata now under consideration is in harmony with the hypothesis that the Paris basin formed a gulf into which several rivers flowed.

EOCENE FORAMINIFERA.

(FIGURE 219. Calcarina rarispina, Desh. a. Natural size. b. Magnified.)

(FIGURE 220. Spirolina stenostoma, Desh. a. Natural size. b. Magnified.)

(FIGURE 221. Triloculina inflata, Desh. a. Natural size. b. Magnified.)

In some parts of the calcaire grossier round Paris, certain beds occur of a stone used in building, and called by the French geologists "Miliolite limestone." It is almost entirely made up of millions of microscopic shells, of the size of minute grains of sand, which all belong to the class Foraminifera. Figures of some of these are given in Figures 219 to 221. As this miliolitic stone never occurs in the Faluns, or Upper Miocene strata of Brittany and Touraine, it often furnishes the geologist with a useful criterion for distinguishing the detached Eocene and Upper Miocene formations scattered over those and other adjoining provinces. The discovery of the remains of Palaeotherium and other mammalia in some of the upper beds of the calcaire grossier shows that these land animals began to exist before the deposition of the overlying gypseous series had commenced.

LOWER CALCAIRE GROSSIER, OR GLAUCONIE GROSSIERE (B.1 TABLE 16.1).

The lower part of the calcaire grossier, which often contains much green earth, is characterised at Auvers, near Pontoise, to the north of Paris, and still more in the environs of Compiegne, by the abundance of nummulites, consisting chiefly of N. laevigata, N. scabra, and N. Lamarcki, which constitute a large proportion of some of the stony strata, though these same foraminifera are wanting in beds of similar age in the immediate environs of Paris.

SOISSONNAIS SANDS, OR LITS COQUILLIERS (B.2 TABLE 16.1).

(FIGURE 222. Nerita conoidea, Lam. Syn. N. Schmidelliana, Chemnitz.)

Below the preceding formation, shelly sands are seen, of considerable thickness, especially at Cuisse-Lamotte, near Compiegne, and other localities in the Soissonnais, about fifty miles N.E. of Paris, from which about 300 species of shells have been obtained, many of them common to the calcaire grossier and the Bracklesham beds of England, and many peculiar. The Nummulites planulata is very abundant, and the most characteristic shell is the Nerita conoidea, Lam., a fossil which has a very wide geographical range; for, as M. d'Archiac remarks, it accompanies the nummulitic formation from Europe to India, having been found in Cutch, near the mouths of the Indus, associated with Nummulites scabra. No less than 33 shells of this group are said to be identical with shells of the London clay proper, yet, after visiting Cuisse-Lamotte and other localities of the "Sables inferieurs" of Archiac, I agree with Mr. Prestwich, that the latter are probably newer than the London clay, and perhaps older than the Bracklesham beds of England. The London clay seems to be unrepresented in the Paris basin, unless partially so, by these sands. (d'Archiac Bulletin tome 10 and Prestwich Quarterly Geological Journal 1847 page 377.)

LOWER EOCENE FORMATIONS OF FRANCE.

ARGILE PLASTIQUE (C.2 TABLE 16.1).

At the base of the tertiary system in France are extensive deposits of sands, with occasional beds of clay used for pottery, and called "argile plastique." Fossil oysters (Ostrea bellovacina) abound in some places, and in others there is a mixture of fluviatile shells, such as Cyrena cuneiformis (Figure 216), Melania inquinata (Figure 217), and others, frequently met with in beds occupying the same position in the London Basin. Layers of lignite also accompany the inferior clays and sands.

Immediately upon the chalk at the bottom of all the tertiary strata in France there generally is a conglomerate or breccia of rolled and angular chalk-flints, cemented by siliceous sand. These beds appear to be of littoral origin, and imply the previous emergence of the chalk, and its waste by denudation. In the year 1855, the tibia and femur of a large bird equalling at least the ostrich in size were found at Meudon, near Paris, at the base of the Plastic clay. This bird, to which the name of Gastornis Parisiensis has been assigned, appears, from the Memoirs of MM. Hebert, Lartet, and Owen, to belong to an extinct genus. Professor Owen refers it to the class of wading land birds rather than to an aquatic species. (Quarterly Geological Journal volume 12 page 204 1856.)

That a formation so much explored for economical purposes as the Argile plastique around Paris, and the clays and sands of corresponding age near London, should never have afforded any vestige of a feathered biped previously to the year 1855, shows what diligent search and what skill in osteological interpretation are required before the existence of birds of remote ages can be established.

SABLES DE BRACHEUX (C.3 TABLE 16.1).

The marine sands called the Sables de Bracheux (a place near Beauvais), are considered by M. Hebert to be older than the Lignites and Plastic clay, and to coincide in age with the Thanet Sands of England. At La Fere, in the Department of Aisne, in a deposit of this age, a fossil skull has been found of a quadruped called by Blainville Arctocyon primaevus, and supposed by him to be related both to the bear and to the Kinkajou (Cercoleptes). This creature appears to be the oldest known tertiary mammifer.

NUMMULITIC FORMATIONS OF EUROPE, ASIA, ETC.

Of all the rocks of the Eocene period, no formations are of such great geographical importance as the Upper and Middle Eocene, as above defined, assuming that the older tertiary formation, commonly called nummulitic, is correctly ascribed to this group. It appears that of more than fifty species of these foraminifera described by D'Archiac, one or two species only are found in other tertiary formations whether of older or newer date. Nummulites intermedia, a Middle Eocene form, ascends into the Lower Miocene, but it seems doubtful whether any species descends to the level of the London clay, still less to the Argile plastique or Woolwich beds. Separate groups of strata are often characterised by distinct species of nummulite; thus the beds between the lower Miocene and the lower Eocene may be divided into three sections, distinguished by three different species of nummulites, N. variolaria in the upper, N. laevigata in the middle, and N. planulata in the lower beds. The nummulitic limestone of the Swiss Alps rises to more than 10,000 feet above the level of the sea, and attains here and in other mountain chains a thickness of several thousand feet. It may be said to play a far more conspicuous part than any other tertiary group in the solid framework of the earth's crust, whether in Europe, Asia, or Africa. It occurs in Algeria and Morocco, and has been traced from Egypt, where it was largely quarried of old for the building of the Pyramids, into Asia Minor, and across Persia by Bagdad to the mouths of the Indus. It has been observed not only in Cutch, but in the mountain ranges which separate Scinde from Persia, and which form the passes leading to Caboul; and it has been followed still farther eastward into India, as far as eastern Bengal and the frontiers of China.

(FIGURE 223. Nummulites Puschi, D'Archiac. Peyrehorade, Pyrenees. a. External surface of one of the nummulites, of which longitudinal sections are seen in the limestone. b. Transverse section of same.)

Dr. T. Thompson found nummulites at an elevation of no less than 16,500 feet above the level of the sea, in Western Thibet. One of the species, which I myself found very abundant on the flanks of the Pyrenees, in a compact crystalline marble (Figure 223) is called by M. D'Archiac Nummulites Puschi. The same is also very common in rocks of the same age in the Carpathians. In many distant countries, in Cutch, for example, some of the same shells, such as Nerita conoidea (Figure 222), accompany the nummulites, as in France. The opinion of many observers, that the Nummulitic formation belongs partly to the cretaceous era, seems chiefly to have arisen from confounding an allied genus, Orbitoides, with the true Nummulite.

When we have once arrived at the conviction that the nummulitic formation occupies a middle and upper place in the Eocene series, we are struck with the comparatively modern date to which some of the greatest revolutions in the physical geography of Europe, Asia, and Northern Africa must be referred. All the mountain-chains, such as the Alps, Pyrenees, Carpathians, and Himalayas, into the composition of whose central and loftiest parts the nummulitic strata enter bodily, could have had no existence till after the Middle Eocene period. During that period the sea prevailed where these chains now rise, for nummulites and their accompanying testacea were unquestionably inhabitants of salt water. Before these events, comprising the conversion of a wide area from a sea to a continent, England had been peopled, as I before pointed out, by various quadrupeds, by herbivorous pachyderms, by insectivorous bats, and by opossums.

Almost all the volcanoes which preserve any remains of their original form, or from the craters of which lava streams can be traced, are more modern than the Eocene fauna now under consideration; and besides these superficial monuments of the action of heat, Plutonic influences have worked vast changes in the texture of rocks within the same period. Some members of the nummulitic and overlying tertiary strata called flysch have actually been converted in the central Alps into crystalline rocks, and transformed into marble, quartz-rock, micha-schist, and gneiss. (Murchison Quarterly Journal of Geological Society volume 5 and Lyell volume 6 1850 Anniversary Address.)

EOCENE STRATA IN THE UNITED STATES.

In North America the Eocene formations occupy a large area bordering the Atlantic, which increases in breadth and importance as it is traced southward from Delaware and Maryland to Georgia and Alabama. They also occur in Louisiana and other States both east and west of the valley of the Mississippi. At Claiborne, in Alabama, no less than 400 species of marine shells, with many echinoderms and teeth of fish, characterise one member of this system. Among the shells, the Cardita planicosta, before mentioned (Figure 191), is in abundance; and this fossil and some others identical with European species, or very nearly allied to them, make it highly probable that the Claiborne beds agree in age with the central or Bracklesham group of England, and with the calcaire grossiere of Paris. (See paper by the Author Quarterly Journal of Geological Society volume 4 page 12 and Second Visit to the United States volume 2 page 59.)

Higher in the series is a remarkable calcareous rock, formerly called "the nummulite limestone," from the great number of discoid bodies resembling nummulites which it contains, fossils now referred by A. d'Orbigny to the genus Orbitoides, which has been demonstrated by Dr. Carpenter to belong to the foraminifera. (Quarterly Journal of Geological Society volume 6 page 32.) That naturalist, moreover, is of opinion that the Orbitoides alluded to (O. Mantelli) is of the same species as one found in Cutch, in the Middle Eocene or nummulitic formation of India.

Above the orbitoidal limestone is a white limestone, sometimes soft and argillaceous, but in parts very compact and calcareous. It contains several peculiar corals, and a large Nautilus allied to N. ziczac; also in its upper bed a gigantic cetacean, called Zeuglodon by Owen. (See Memoir by R.W. Gibbes Journal of Academy of Natural Science Philadelphia volume 1 1847.)

The colossal bones of this cetacean are so plentiful in the interior of Clarke County, Alabama, as to be characteristic of the formation. The vertebral column of one skeleton found by Dr. Buckley at a spot visited by me, extended to the length of nearly seventy feet, and not far off part of another backbone nearly fifty feet long was dug up. I obtained evidence, during a short excursion, of so many localities of this fossil animal within a distance of ten miles, as to lead me to conclude that they must have belonged to at least forty distinct individuals.

(FIGURE 224. Zeuglodon cetoides, Owen. Basilosaurus, Harlan. Molar tooth, natural size.)

(FIGURE 225. Zeuglodon cetoides, Owen. Basilosaurus, Harlan. Vertebra, reduced.)

Professor Owen first pointed out that this huge animal was not reptilian, since each tooth was furnished with double roots (Figure 224), implanted in corresponding double sockets; and his opinion of the cetacean nature of the fossil was afterwards confirmed by Dr. Wyman and Dr. R.W. Gibbes. That it was an extinct mammal of the whale tribe has since been placed beyond all doubt by discovery of the entire skull of another fossil species of the same family, having the double occipital condyles only met with in mammals, and the convoluted tympanic bones which are characteristic of cetaceans.

CHAPTER XVII.

UPPER CRETACEOUS GROUP.

Lapse of Time between Cretaceous and Eocene Periods. Table of successive Cretaceous Formations. Maestricht Beds. Pisolitic Limestone of France. Chalk of Faxoe. Geographical Extent and Origin of the White Chalk. Chalky Matter now forming in the Bed of the Atlantic. Marked Difference between the Cretaceous and existing Fauna. Chalk-flints. Pot-stones of Horstead. Vitreous Sponges in the Chalk. Isolated Blocks of Foreign Rocks in the White Chalk supposed to be ice-borne. Distinctness of Mineral Character in contemporaneous Rocks of the Cretaceous Epoch. Fossils of the White Chalk. Lower White Chalk without Flints. Chalk Marl and its Fossils. Chloritic Series or Upper Greensand. Coprolite Bed near Cambridge. Fossils of the Chloritic Series. Gault. Connection between Upper and Lower Cretaceous Strata. Blackdown Beds. Flora of the Upper Cretaceous Period. Hippurite Limestone. Cretaceous Rocks in the United States.

We have treated in the preceding chapters of the Tertiary or Cainozoic strata, and have next to speak of the Secondary or Mesozoic formations. The uppermost of these last is commonly called the chalk or the cretaceous formation, from creta, the latin name for that remarkable white earthy limestone, which constitutes an upper member of the group in those parts of Europe where it was first studied. The marked discordance in the fossils of the tertiary, as compared with the cretaceous formations, has long induced many geologists to suspect that an indefinite series of ages elapsed between the respective periods of their origin. Measured, indeed, by such a standard, that is to say, by the amount of change in the Fauna and Flora of the earth effected in the interval, the time between the Cretaceous and Eocene may have been as great as that between the Eocene and Recent periods, to the history of which the last seven chapters have been devoted. Several deposits have been met with here and there, in the course of the last half century, of an age intermediate between the white chalk and the plastic clays and sands of the Paris and London districts, monuments which have the same kind of interest to a geologist which certain medieval records excite when we study the history of nations. For both of them throw light on ages of darkness, preceded and followed by others of which the annals are comparatively well-known to us. But these newly-discovered records do not fill up the wide gap, some of them being closely allied to the Eocene, and others to the Cretaceous type, while none appear as yet to possess so distinct and characteristic a fauna as may entitle them to hold an independent place in the great chronological series.

Among the formations alluded to, the Thanet Sands of Prestwich have been sufficiently described in the last chapter, and classed as Lower Eocene. To the same tertiary series belong the Belgian formations, called by Professor Dumont, Landenian. On the other hand, the Maestricht and Faxoe limestones are very closely connected with the chalk, to which also the Pisolitic limestone of France is referable.

CLASSIFICATION OF THE CRETACEOUS ROCKS.

TABLE 17.1.

UPPER CRETACEOUS OR CHALK PERIOD.

1. Maestricht Beds and Faxoe Limestone. 2. Upper White Chalk, with flints. 3. Lower White Chalk, without flints. 4. Chalk Marl. 5. Chloritic series (or Upper Greensand). 6. Gault.

LOWER CRETACEOUS OR NEOCOMIAN.

1. Marine: Upper Neocomian, see Chapter 18. Fresh-water: Wealden Beds (upper part). 2. Marine: Middle Neocomian, see Chapter 18. Fresh-water: Wealden Beds (upper part). 3. Marine: Lower Neocomian, see Chapter 18. Fresh-water: Wealden Beds (upper part).

The cretaceous group has generally been divided into an Upper and a Lower series, the Upper called familiarly THE CHALK, and the Lower THE GREENSAND; the one deriving its name from the predominance of white earthy limestone and marl, of which it consists in a great part of France and England, the other or lower series from the plentiful mixture of green or chloritic grains contained in some of the sands and cherts of which it largely consists in the same countries. But these mineral characters often fail, even when we attempt to follow out the same continuous subdivisions throughout a small portion of the north of Europe, and are worse than valueless when we desire to apply them to more distant regions. It is only by aid of the organic remains which characterise the successive marine subdivisions of the formation that we are able to recognise in remote countries, such as the south of Europe or North America, the formations which were there contemporaneously in progress. To the English student of geology it will be sufficient to begin by enumerating those groups which characterise the series in this country and others immediately contiguous, alluding but slightly to those of more distant regions. In Table 17.1 it will be seen that I have used the term Neocomian for that commonly called "Lower Greensand;" as this latter term is peculiarly objectionable, since the green grains are an exception to the rule in many of the members of this group even in districts where it was first studied and named.

MAESTRICHT BEDS.

(FIGURE 226. Belemnitella mucronata, Maestricht, Faxoe, and White Chalk. a. Entire specimen, showing vascular impression on outer surface, and characteristic slit. b. Section of same, showing place of phragmocone. (For particulars of structure see Chapter 18.))

On the banks of the Meuse, at Maestricht, reposing on ordinary white chalk with flints, we find an upper calcareous formation about 100 feet thick, the fossils of which are, on the whole, very peculiar, and all distinct from tertiary species. Some few are of species common to the inferior white chalk, among which may be mentioned Belemnitella mucronata (Figure 226) and Pecten quadricostatus, a shell regarded by many as a mere variety of Pecten quinquecostatus (see Figure 270). Besides the Belemnite there are other genera, such as Baculites and Hamites, never found in strata newer than the cretaceous, but frequently met with in these Maestricht beds. On the other hand, Voluta, Fasciolaria, and other genera of univalve shells, usually met with only in tertiary strata, occur.

The upper part of the rock, about 20 feet thick, as seen in St. Peter's Mount, in the suburbs of Maestricht, abounds in corals and Bryozoa, often detachable from the matrix; and these beds are succeeded by a soft yellowish limestone 50 feet thick, extensively quarried from time immemorial for building. The stone below is whiter, and contains occasional nodules of grey chert or chalcedony.

(FIGURE 227. Mosasaurus Camperi. Original more than three feet long.)

(FIGURE 228. Hemipneustes radiatus, Ag. Spatangus radiatus, Lam. Chalk of Maestricht and white chalk.)

M. Bosquet, with whom I examined this formation (August, 1850), pointed out to me a layer of chalk from two to four inches thick, containing green earth and numerous encrinital stems, which forms the line of demarkation between the strata containing the fossils peculiar to Maestricht and the white chalk below. The latter is distinguished by regular layers of black flint in nodules, and by several shells, such as Terebratula carnea (see Figure 246), wholly wanting in beds higher than the green band. Some of the organic remains, however, for which St. Peter's Mount is celebrated, occur both above and below that parting layer, and, among others, the great marine reptile called Mosasaurus (see Figure 227), a saurian supposed to have been 24 feet in length, of which the entire skull and a great part of the skeleton have been found. Such remains are chiefly met with in the soft freestone, the principal member of the Maestricht beds. Among the fossils common to the Maestricht and white chalk may be instanced the echinoderm, Figure 228.

I saw proofs of the previous denudation of the white chalk exhibited in the lower bed of the Maestricht formation in Belgium, about 30 miles S.W. of Maestricht, at the village of Jendrain, where the base of the newer deposit consisted chiefly of a layer of well-rolled, black chalk-flint pebbles, in the midst of which perfect specimens of Thecidea papillata and Belemnitella mucronata are imbedded. To a geologist accustomed in England to regard rolled pebbles of chalk-flint as a common and distinctive feature of tertiary beds of different ages, it is a new and surprising phenomenon to behold strata made up of such materials, and yet to feel no doubt that they were accumulated in a sea in which the belemnite and other cretaceous mollusca flourished.

PISOLITIC LIMESTONE OF FRANCE.

Geologists were for many years at variance respecting the chronological relations of this rock, which is met with in the neighbourhood of Paris, and at places north, south, east, and west of that metropolis, as between Vertus and Laversines, Meudon and Montereau. By many able palaeontologists the species of fossils, more than fifty in number, were declared to be more Eocene in their appearance than Cretaceous. But M. Hebert found in this formation at Montereau, near Paris, the Pecten quadricostatus, a well-known Cretaceous species, together with some other fossils common to the Maestricht chalk and to the Baculite limestone of the Cotentin, in Normandy. He therefore, as well as M. Alcide d'Orbigny, who had carefully studied the fossils, came to the opinion that it was an upper member of the Cretaceous group. It is usually in the form of a coarse yellowish or whitish limestone, and the total thickness of the series of beds already known is about 100 feet. Its geographical range, according to M. Hebert, is not less than 45 leagues from east to west, and 35 from north to south. Within these limits it occurs in small patches only, resting unconformably on the white chalk.

(FIGURE 229. Portion of Baculites Faujasii. Maestricht and Faxoe beds and white chalk.)

(FIGURE 230. Nautilus Danicus, Schl. Faxoe, Denmark.)

The Nautilus Danicus, Figure 230, and two or three other species found in this rock, are frequent in that of Faxoe, in Denmark, but as yet no Ammonites, Hamites, Scaphites, Turrilites, Baculites, or Hippurites have been met with. The proportion of peculiar species, many of them of tertiary aspect, is confessedly large; and great aqueous erosion suffered by the white chalk, before the pisolitic limestone was formed, affords an additional indication of the two deposits being widely separated in time. The pisolitic formation, therefore, may eventually prove to be somewhat more intermediate in date between the secondary and tertiary epochs than the Maestricht rock.

CHALK OF FAXOE.

In the island of Seeland, in Denmark, the newest member of the chalk series, seen in the sea-cliffs at Stevensklint resting on white chalk with flints, is a yellow limestone, a portion of which, at Faxoe, where it is used as a building stone, is composed of corals, even more conspicuously than is usually observed in recent coral reefs. It has been quarried to the depth of more than 40 feet, but its thickness is unknown. The imbedded shells are chiefly casts, many of them of univalve mollusca, which are usually very rare in the white chalk of Europe. Thus, there are two species of Cypraea, one of Oliva, two of Mitra, four of the genus Cerithium, six of Fusus, two of Trochus, one of Patella, one of Emarginula, etc.; on the whole, more than thirty univalves, spiral or patelliform. At the same time, some of the accompanying bivalve shells, echinoderms, and zoophytes, are specifically identical with fossils of the true Cretaceous series. Among the cephalopoda of Faxoe may be mentioned Baculites Faujasii (Figure 229), and Belemnitella mucronata (Figure 226), shells of the white chalk. The Nautilus Danicus (see Figure 230) is characteristic of this formation; and it also occurs in France in the calcaire pisolitique of Laversin (Department of Oise). The claws and entire skull of a small crab, Brachyurus rugosus (Schlott.), are scattered through the Faxoe stone, reminding us of similar crustaceans inclosed in the rocks of modern coral reefs. Some small portions of this coralline formation consist of white earthy chalk.

COMPOSITION, EXTENT AND ORIGIN OF THE WHITE CHALK.

(FIGURE 231. Diagrammatic section from Hertfordshire, in England, to Sens, in France. Through London (left), Hythe, Boulogne, Valley of Bray, Paris and Sens (right).)

The highest beds of chalk in England and France consist of a pure, white, calcareous mass, usually too soft for a building-stone, but sometimes passing into a more solid state. It consists, almost purely, of carbonate of lime; the stratification is often obscure, except where rendered distinct by interstratified layers of flint, a few inches thick, occasionally in continuous beds, but oftener in nodules, and recurring at intervals generally from two to four feet distant from each other. This upper chalk is usually succeeded, in the descending order, by a great mass of white chalk without flints, below which comes the chalk marl, in which there is a slight admixture of argillaceous matter. The united thickness of the three divisions in the south of England equals, in some places, 1000 feet. The section in Figure 231 will show the manner in which the white chalk extends from England into France, covered by the tertiary strata described in former chapters, and reposing on lower cretaceous beds.

The area over which the white chalk preserves a nearly homogeneous aspect is so vast, that the earlier geologists despaired of discovering any analogous deposits of recent date. Pure chalk, of nearly uniform aspect and composition, is met with in a north-west and south-east direction, from the north of Ireland to the Crimea, a distance of about 1140 geographical miles, and in an opposite direction it extends from the south of Sweden to the south of Bordeaux, a distance of about 840 geographical miles. In Southern Russia, according to Sir R. Murchison, it is sometimes 600 feet thick, and retains the same mineral character as in France and England, with the same fossils, including Inoceramus Cuvieri, Belemnitella mucronata, and Ostrea vesicularis (Figure 251).

(Figures 232 to 236.— Organic bodies forming the ooze of the bed of the Atlantic at great depths.

(FIGURE 232. Globigerina bulloides. Calcareous Rhizopod.)

(FIGURE 233. Actinocyclus. Siliceous Diatomaceae. )

(FIGURE 234. Pinnularia. Siliceous Diatomaceae.)

(FIGURE 235. Eunotia bidens. Siliceous Diatomaceae.)

(FIGURE 236. Spicula of sponge. Siliceous sponge.))

Great light has recently been thrown upon the origin of the unconsolidated white chalk by the deep soundings made in the North Atlantic, previous to laying down, in 1858, the electric telegraph between Ireland and Newfoundland. At depths sometimes exceeding two miles, the mud forming the floor of the ocean was found, by Professor Huxley, to be almost entirely composed (more than nineteen- twentieths of the whole) of minute Rhizopods, or foraminiferous shells of the genus Globigerina, especially the species Globigerina bulloides (see Figure 232.) the organic bodies next in quantity were the siliceous shells called Polycystineae, and next to them the siliceous skeletons of plants called Diatomaceae (Figures 233, 234, 235), and occasionally some siliceous spiculae of sponges (Figure 236) were intermixed. These were connected by a mass of living gelatinous matter to which he has given the name of Bathybius, and which contains abundance of very minute bodies termed Coccoliths and Coccospheres, which have also been detected fossil in chalk.

Sir Leopold MacClintock and Dr. Wallich have ascertained that 95 per cent of the mud of a large part of the North Atlantic consists of Globigerina shells. But Captain Bullock, R.N., lately brought up from the enormous depth of 16,860 feet a white, viscid, chalky mud, wholly devoid of Globigerinae. This mud was perfectly homogeneous in composition, and contained no organic remains visible to the naked eye. Mr. Etheridge, however, has ascertained by microscopical examination that it is made up of Coccoliths, Discoliths, and other minute fossils like those of the Chalk classed by Huxley as Bathybius, when this term is used in its widest sense. This mud, more than three miles deep, was dredged up in latitude 20 degrees 19' N., longitude 4 degrees 36' E., or about midway between Madeira and the Cape of Good Hope.

The recent deep-sea dredgings in the Atlantic conducted by Dr. Wyville Thomson, Dr. Carpenter, Mr. Gwyn Jeffreys, and others, have shown that on the same white mud there sometimes flourish Mollusca, Crustacea, and Echinoderms, besides abundance of siliceous sponges, forming, on the whole, a marine fauna bearing a striking resemblance in its general character to that of the ancient chalk.

POPULAR ERROR AS TO THE GEOLOGICAL CONTINUITY OF THE CRETACEOUS PERIOD.

We must be careful, however, not to overrate the points of resemblance which the deep-sea investigations have placed in a strong light. They have been supposed by some naturalists to warrant a conclusion expressed in these words: "We are still living in the Cretaceous epoch;" a doctrine which has led to much popular delusion as to the bearing of the new facts on geological reasoning and classification. The reader should be reminded that in geology we have been in the habit of founding our great chronological divisions, not on foraminifera and sponges, nor even on echinoderms and corals, but on the remains of the most highly organised beings available to us, such as the mollusca; these being met with, as explained in Chapter 9, in stratified rocks of almost every age. In dealing with the mollusca, it is those of the highest or most specialised organisation, which afford us the best characters in proportion as their vertical range is the most limited. Thus the Cephalopoda are the most valuable, as having a more restricted range in time than the Gasteropoda; and these, again, are more characteristic of the particular stratigraphical subdivisions than are the Lamellibranchiate Bivalves, while these last, again, are more serviceable in classification than the Brachiopoda, a still lower class of shell-fish, which are the most enduring of all.

When told that the new dredgings prove that "we are still living in the Chalk Period," we naturally ask whether some cuttle-fish has been found with a Belemnite forming part of its internal framework; or have Ammonites, Baculites, Hamites, Turrilites, with four or five other Cephalopodous genera characteristic of the chalk and unknown as tertiary, been met with in the abysses of the ocean? Or, in the absence of these long-extinct forms, has a single spiral univalve, or species of Cretaceous Gasteropod, been found living? Or, to descend still lower in the scale, has some characteristic Cretaceous genus of Lamellibranchiate Bivalve, such as the Inoceramus, or Hippurite, foreign to the Tertiary seas, been proved to have survived down to our time? Or, of the numerous genera of lamellibranchiates common to the Cretaceous and Recent seas, has one species been found living? The answer to all these questions is— not one has been found. Even of the humblest shell-fish, the Brachiopods, no new species common to the Cretaceous and recent seas has yet been met with. It has been very generally admitted by conchologists that out of a hundred species of this tribe occurring fossil in the Upper Chalk— one, and one only, Terebratulina striata, is still living, being thought to be identical with Terebratula caput-serpentis. Although this identity is still questioned by some naturalists of authority, it would certainly not surprise us if another lamp-shell of equal antiquity should be met with in the deep sea.