Those persons who have been so unfortunate as to permit themselves to accept a ready made opinion of dangers and roughness to be met with in the more newly settled regions, might find a tour of the Hills doubly interesting by making a supplementary study of "The Living Age," which cannot be so correctly viewed from a distance as is sometimes supposed, since the specimens exhibited are not always a true average of the strata they are supposed to represent.
CHAPTER XVI.
CONCLUSION.
After a visit to the marvelous caverns of the Black Hills, much may be added to the pleasure already enjoyed, through the explanatory activity of the Yellowstone National Park, where even the wonderful combinations of beauty and grandeur are by no means the full measure of attraction and charm. Here is found evidence to verify theories concerning the caves, and those theories in turn contribute in no small degree to a satisfactory understanding of the mysteries of geyser action. For scientific study the two regions should be taken together, since the natural conditions are practically the same, and the chief difference lies in the stages of development; the present of the Park explaining the recent past of the Hills, while the present of the Hills foretells the future of the Park. It seems that Nature, with a full appreciation of the limits and restrictions binding our powers to penetrate certain secrets of an intermittent force, has in this great western country carefully prepared what might quite properly be termed a progressive course of study, wherein each locality makes plain a special point that somewhere else appears obscure.
As has been said in the preceding chapters, the two great caves in the Black Hills of South Dakota cannot be accounted for by the same methods as are recognized as being responsible for the slow excavation of the best known caves of the United States. Although there is every indication that both these caves have been subject to the action of enormous volumes of water, there is equally positive evidence that neither was ever the scene of a flowing cave-river. The lowest levels in both show the narrowest fissures and the heaviest deposits of crystal, by which we infer that the water was held in confinement here, while all the higher passages or channels bear witness to the water's flow. But many of these channels in Crystal Cave, or indeed we might say, most of them, present an unmistakable record of the gauge of the water stage at different periods. During the earlier time, when the volume of water and consequent pressure were greatest, frictional motion must have been limited to the main channel connecting with the vent, and the high gauge of water maintained a fairly uniform degree of heat near its surface. In consequence of these conditions geyser action, probably, was constant, and chemical activity was such that great chambers were formed and then decorated, as already described, with wonderful masses of crystal. As the water gauge receded to lower levels the higher chambers became storage basins for water and steam forced up by the pressure from below, and the time required for these to fill and accumulate sufficient pressure to continue the ejectment, formed the periods between eruptions after the geyser became intermittent. It was during this stage that the sharp crystals in many of the channels, now called passages, were worn down to smooth surfaces; and later, when water occupied only the lowest level, and the great geyser had become reduced to merely a steam vent, the channels immediately connecting with that level were in their turn subjected to the same smoothing process, and then all action ceased.
As no two of the glorious geysers of the Yellowstone Park are alike, neither do the two great caves of the Hills indicate that they should be so. The vent-tubing of each is quite unlike that of the other in all the essential governing points of length, size, shape, angle of inclination and power-conserving bends. And the differences extend in an almost equally marked degree throughout the vast and complicated succession of storage chambers and their connecting channels. The small vent of Wind Cave shows that the ejected jet was far from being equal to that of the Crystal Cave in volume; but the nearly perpendicular long arm of its tube shows also that its jet attained a much greater height, even supposing that it should be necessary to make some allowance for a short elbow at the top.
Dr. Hayden's geological party gave much attention to the Yellowstone Park while its wonders were new to the world, and observations were made at various times during the period included between the years 1869 and 1870. The special study, and full report of the geysers became the duty of Dr. A. C. Peal, whose descriptions and conclusions were published in U. S. Geological Survey Report, 1878, Part II. In the final pages of his report he quotes the leading authorities on geyser action, and applies the principles of their theories, according to his own judgment, to the geysers of the park. Since copies of this report are not now easily obtained, nor even always accessible to the increasing number of personages who visit the park, it may be well to quote from him some of the theories he discussed and the opinions he expressed. On page 416, beginning the chapter with the derivation of the word geyser from the Icelandic word geysa—to gush, he continues:
"We now come to the definition of a geyser. It may be defined to be a periodically eruptive or intermittent hot spring, from which the water is projected into the air in a fountain-like column. The analogy between geysers and volcanoes has frequently been noticed and the former have often been described as volcanoes which erupt heated water instead of melted lava. We have italicized the word hot in the definition just given, because springs containing a large amount of gas may simulate geysers.