"'When so much vapor has escaped that the expansive force of that which remains has become less than the pressure of the confining column of water, tranquility is restored, and this lasts until such a quantity of vapor is again collected as to produce a fresh eruption. The spouting of the spring is therefore repeated at intervals, depending on the capacity of the cavern, the height of the column of water, and the heat generated below.'" Dr. Peal continues:

"Bishof says that the eruptions of the Geyser and Strockr agree exactly with this explanation and he accounts for the two distinct classes of eruption observed in the Geyser as follows:

"'The two distinct classes of eruption in the geyser which we have already mentioned seem to be attributable to two different cavities. A small cavity fills quicker, and, therefore, empties itself more frequently; a larger one fills slower, empties itself seldomer, but with greater violence.'"

Bunsen's theory is the next considered and is somewhat similar to Bischof's but with notable differences. After taking temperatures at different points in the Geyser tube his first conclusions are that:

(1) The temperature in the geyser tube increases as we descend.

(2) At no point does the water in the tube attain the temperature of ebullition which it should have under the pressure to which it is subjected, but the temperature depends on the time that has elapsed since the last eruption. As a great eruption comes near it approaches the boiling point.

(3) At the depth of about forty-five feet the difference between the temperature of the water and the calculated boiling point for that pressure is the least.

The main point of his theory appears to be that an eruption takes place when the water in the tube reaches the boiling point, and to account for it, "He supposes that the column in the central tube communicates by a long and sinuous channel with some space, be it what it may, which is subjected to the action of the direct source of subterranean heat. The temperature gets raised above the boiling point, due to the pressure, and a sudden generation of steam is the result. This steam rises in the column of water, which, being cooler, causes it to condense. Gradually the heat of the water is raised until the water of the channel must boil, and the steam therefore cannot condense, but must accumulate and acquire a gradually increasing tension. The condensation of the bubbles possesses a periodic character, and to this is due the uplifting of the water in what Bunsen calls conical water hills, which are accompanied by the subterranean explosions."

Prof. Comstock is quoted as thinking "Bunsen's theory has not yet been proved adequate to explain the more prominent features of geyser eruptions. Nor does it, in his opinion, account for all the differences between geysers and hot springs, and he proposes a structural hypothesis which combines Bischof's and Bunsen's theories."

This hypothesis is illustrated by a figure in which a reservoir partly filled with water is connected with the surface by a tube having a double curve, and he explains that the water collecting in the depressed curve should confine the steam, rising from the reservoir in the other curve until the pressure is sufficient to cause an eruption. His theory of action being that the water in the reservoir remains in equilibrium at a certain level, and the constant heat fills the space above with vapor, which heats the water held in the downward bend of the tube, and that also evolves vapor which fills the balance of the tube to the vent. When the combined pressure of this vapor and water are overcome by the expansion of vapor accumulated above the reservoir, they are forced out, and followed by a portion of the water of the reservoir. This theory is in the report of Captain Jones on Northwestern Wyoming.

The last theory cited by Dr. Peal is that of S. Baring-Gould, "Who visited the Iceland geysers in 1863, and thinks that a bent tube is sufficient to explain the action of the Great Geyser. He took an iron tube and bent it in an angle of 110 deg., keeping one arm half the length of the other. He filled the tube with water and placed the short arm in the fire. For a moment the surface of the liquid remained quiet, and then the pipe began to quiver; a slight overflow took place, without any sign of ebullition, and then suddenly, with a throb, the whole column was forced high into the air. With a tube, the long arm of which measured two feet and the bore of which was three-eighths of an inch, he sent a jet to the height of eighteen feet. Steam is generated in the short arm and presses down the water, causing an overflow until the steam bubble turns the angle, when it forces out the column in the long arm with incredible violence."

Dr. Peal now goes on to say:

"Of the theories that we have just enumerated, perhaps no one is adequate to explain all the phenomena of geyser action. Bunsen's theory comes nearest to it, and in the simplest kinds of geysers is a sufficient explanation. The variations and modifications in the geyser tubes and subterranean water passages must undoubtedly be important factors entering into any complete explanation of geyser action. Now, of course, we can see what the conditions are at the surface, but in our experiments we can penetrate to a very inconsiderable distance. We have, therefore, no data to present on these points, and investigations of this branch of the subject will have to be carried on in an artificial manner; that is artificial geysers will have to be constructed, and various modifications made in the tubes until results are reached analogous to those seen in natural geysers. If water in a glass tube be heated with rapidity from the bottom, it will be expelled from the tube violently, and if boiled in a kettle which has a lid and a spout, either the lid will be blown off or the water will be forced out through the spout. The first case is an illustration, in part at least, of Bunsen's theory, and the second exemplifies the theories which presuppose the existence of subterranean cavities with tubes at or near the surface. According to the former we must suppose that the layer of rock, extending seventy-five to seventy-seven feet below the surface, contains sufficient heat to account for geyseric phenomena; or else that the geyser tube has some opening, either at the bottom or on the sides, by which steam and superheated water have access to it from a considerably greater depth where the temperature is very high. At these depths caverns probably exist." * * * *

"That such cavities exist is more than probable. On page 405 I have indicated my belief, that all geysers are originally due to a violent outburst of steam and water, and under such conditions, irregular cavities and passages are more likely to be formed than regular tubes." * *

"In view of what we have just written, Bunsen's conclusion (No. 2) would have to be modified somewhat. His conclusion was that at no point in the tube did the water attain the temperature of ebullition which it should have under the pressure to which it is subjected. As far as this relates to the straight tube in which his temperatures were taken, it may be so; but if he could have taken temperatures in the side conduit, I have little doubt he would soon have reached a point where the temperature would not only be at the boiling point for that depth but even exceed it. In the Yellowstone Park we obtained a number of surface temperatures which were above the boiling point. In the Great Geyser of Iceland, the mass of water in the tube prevents this condition at the surface, and when it takes place opposite the aperture an eruption is caused. In the main, however, I am inclined to accept Bunsen's theory, especially as it seems to me to require subterranean cavities in which the water must be heated. Whether these are caverns, enlargements of tubes, or sinus channels, appears to me to be of no consequence, except as the interval or period of the geyser might be affected by the form of the reservoir holding the water."

Dr. Peal has reached conclusions which present an imaginary picture of the interior structure of the great geysers of the Park, that bears a striking resemblance to what the two caves of the Black Hills prove to be the true conditions; although it is evident he had in mind caverns of no such vast extent, nor of so complicated a system of cavities and tubes. He overlooked an important feature, however, in not accepting Professor Comstock's idea of the tube having a double curve. The double curve is, or was, conspicuous in both the caves. Unfortunately, its perfection in Wind Cave was necessarily partially sacrificed to make the passage traversable for visitors; but in describing the enormous labor of opening up the cave, Mr. McDonald showed how an arching "crawl" had been worked down by blasting, and the depression beyond filled to raise it to the desired level for securing the present easy passage at the bottom of the main tube, which is the entrance passage. This double curve in the tube is simply the rough original of the S trap of sanitary plumbing. In both caves it is somewhat irregular and deformed, but the familiar "trap" is easily recognized. The destruction of one of the Yellowstone geysers was, no doubt, due to the breaking of the S. One of the many reasons for establishing military control over the Park is said to have been the disastrous results following the introduction of a large quantity of soap into the geyser to cause a premature eruption. The impatience of the party was rewarded by an eruption accompanied by explosions that shook the earth for a great distance, and the geyser has not been seen in action since.

Dr. Peal finds the theories advanced for the generation of steam unsatisfactory and insufficient, especially in the class of geysers having a long steam period. He says: (page 423)

"The Castle Geyser differs from Old Faithful and the Bee Hive mainly in the fact that it has a long steam period, during which the steam pours out or is pushed from the geyser throat with great violence and a terrific noise. There appear to be only two possible explanations of this difference, viz., either an accumulation of immense volumes of steam in the Castle, or an instantaneous formation of steam throughout the length of the geyser tube. The former, to our mind, is untenable, because it seems impossible that the water, which is exhausted in fifteen minutes, should exert enough power to keep down the immense amount of steam that escapes for more than an hour. According to Bunsen's theory, it can be readily explained. The relief afforded by the first part of the eruptions allows the superheated water to rise rapidly, and before it can reach the top or orifice of the tube it is all converted into steam from the top downward with inconceivable rapidity, and must be forced out with the terrific violence which is noted in the case of the Castle. On page 208 we have expressed the opinion that it is the oldest geyser in the region, and it seems to us that a greater length in the tube, with a consequent greater supply of water, will account for the difference between the Castle and Old Faithful, the latter of which we consider one of the youngest geysers in the Upper Geyser Basin."

A study of the Caves in connection with the active Geysers indicates that the theory he suggests and then rejects, is probably the true explanation of the difference between the two kinds of geysers. It seems that the length of the tube must necessarily have more effect on the height of the jet than on the generation of steam; as after an eruption the tube is hotter than at any other time and therefore the generation of steam in it should be less than usual, unless the fresh inflow of water was cold. Then if the storage cavities are broad but low, the steam cannot accumulate above the water; but when the pressure becomes sufficient to force a passage through the tube, the water and steam are expelled together until the pressure is exhausted. But if the storage chambers are vertical fissures, as Wind Cave illustrates, vast quantities of steam must accumulate above the water level in the main reservoirs before the pressure can become sufficient to expel the water in the tube, after which steam alone continues to rush out until the pressure is so relieved that it can no longer force a passage through the water remaining in the trap, when quiet is restored. By the constant addition of fresh water from the surface, by percolation or other usual ways of sinking, the necessary conditions for the generation of steam are maintained with surprising regularity.

The differences in the shape and general arrangement of the cavities and tubes of the two caves, indicate that their action as geysers was very unlike. Wind Cave evidently sent a rather slender column to a great height, nearly perpendicular, and the water eruption was followed by a long steam period. Crystal Cave ejected a much larger jet more frequently, at a low angle of inclination, the eruption was sooner over, and was not followed by a steam period of any consequence.

Thus it can be seen that the caves of the Black Hills prove the theories in regard to geyser action in Yellowstone Park, and those theories, in turn, prove the past history of the caves. The study of geyser action also shows that the conical or dome shape of some of the cave chambers is not due to the whirl of incoming floods, as in other regions, but to jets of water forced up from lower levels.

Perhaps the finest geyser basin, and possible cave, ever in existence was destroyed when the Grand Canon of the Yellowstone became a canon. Evidences of the former conditions in control of this gorgeously brilliant scene are neither wanting nor doubtful. Steam constantly issues from numerous small vents in the canon walls, and a field glass reveals miniature geysers in action down in the depth of the canon, nearly half a mile below the top of the wall; while the entire canon shows, in both the color and character of its rocks, that chemical agencies have wrought changes here that have not been effected in other exposures of similar nature. It seems not improbable that the relation of Yellowstone River to the Grand Canon was the same as, at the present time, is that of the Firehole to the Upper, Middle, and Lower Geyser Basins: and that an explosion of great force was followed by a general collapse instead of the usual eruption of one of the grandest geysers; one result being the sudden precipitation of the river into a new, beautiful, and totally unexpected channel. After its great leap of two hundred and ninety-seven[6] feet at the Lower Fall, the river flows in a brilliant, narrow line of emerald green, broken by the white foam of frequent cascades, between magnificent walls of yellow, white, pink, and red of most vivid hues.

FOOTNOTES:

[6] Measurement by the Hayden Party.

THE END