In order to make the matter perfectly clear, let me say at the very outset that a geyser is simply a volcano from which a quantity of superheated boiling water, saturated with mineral matter, is paroxysmally ejected high into the air. Instead of, as in the case of fire volcanoes, the ejected matters being smoke, flame, lava, scoria, pumice stone, and scalding mud. Moreover, while the eruptions from all volcanoes are intermittent—that is to say, every kind of volcano has alternating periods of activity and repose—the eruptions from[p. 158] geysers further differ from the fire and flame ejections of burning mountains, with their other attendant phenomena, in occurring at definite periods of time, and being of equally definite durations. It is this life-like periodicity in the geyser's mode of action which makes it as awe-inspiring to behold as it is puzzling to explain.
That hot water should issue in a continuous and but little varying sized stream from the bowels of the earth, with a force sufficient to carry it high into the air, has nothing whatever wonderful about it. Such a natural phenomenon may be witnessed at many places. For example, it may be seen doing so everyday at the white foaming, frothing, natural mineral water sprudel of Nauheim, or at any artificially bored artesian well, such as the celebrated one at Paris. Nor does the mere intermittence of water issuing from the bowels of the earth suffice to surprise one. For such natural phenomena are seen at Bolder-Born, in Westphalia; the Lay-Well, at Torbay; the Giggleswick Well, in Yorkshire; and even on a small scale at St Anthony's Well, Arthur's Seat, Edinburgh; all which occurrences are readily explicable on ordinary hydraulic principles, and quite different things from geyser action, which try to explain it as you will, always runs into a volcanic groove. Yet the periodicity of a geyser's action cannot be said to be entirely due to volcanic agency. For the mere action of heat on the solids of the earth's crust, or even of heat in simple conjunction with water, according to either[p. 159] Mackenzie or Tyndall's theories,[] even did they suffice to give a satisfactory explanation of the action of the geysers in Iceland, are assuredly totally inadequate to explain the action of all those of the Yellowstone Park. For the simple reason that the vapours escaping from some of them are so strongly impregnated with hydrochloric, sulphurous, and sulphuric acid gases, as well as with sulphuretted hydrogen, as to compel one to believe that chemical action plays a not unimportant part in the production of the phenomena there witnessed. Moreover, the solids brought up by the water closely resemble in chemical composition the lava ejected from burning mountains, inasmuch as, besides containing a large percentage of silica and alumina, they likewise consist of lime, potash, soda, magnesia, and iron, as well as of a small proportion of other metals, as was guessed at by the beautifully varied green, rose, yellow, and purple hues of the beds of the streamlets flowing from the craters of the geysers. The geysers of the Yellowstone, although situated at the height of 7765 feet above the level of the sea, nevertheless lie in valleys, for the mountains surrounding them are much higher still.
[] Sir G. S. Mackenzie's 'Travels in Iceland,' in 1810, p. 228. Prof. Tyndall 'On Heat,' p. 126.
Some idea of the force with which the water issues from the earth, may be formed from the fact that it is in some cases sufficient to carry a column of over six feet in diameter 200 feet high, for the[p. 160] space of twenty minutes at a time. And all know that 200 feet is nearly double the height of any ordinary church steeple. Moreover, the amount of solids brought up with the water may be imagined when I say that, in one of the boiling springs, the mixture so closely resembles thick milk gruel as to have given to it the name of the 'paint-pot,' and so loaded is its water with mineral matters, that they consolidate almost immediately after escaping from the spring's outlet. So thick indeed is it, that I kneaded some into the shape of a brick, which I have still in my possession. All the geyser water in this district is so charged with silicious earths that it consolidates sufficiently rapidly to form an upright rim around each geyser's vent. Just as a fringe of scoria and lava encircles the mouth of a burning mountain.
The rapidity with which the deposits form and solidify may be conjectured when I say that I saw trees growing close to some of the geysers whose stems and lower branches were so encrusted with geyserite as to give the idea that they were actually petrified. While again I saw an old horse shoe, which had only been fourteen days in the water, so completely enveloped with it that it looked exactly as if it had been hewn out of solid marble.
The mere glancing around, and noticing how the geysers had evidently, like human beings, but a transient existence, produced a somewhat strange sensation. For it was perfectly evident that they are born but to die. All of them appearing to spout[p. 161] themselves permanently out. For while on one side some seemed just as if they were starting into existence, on another were those apparently in the very zenith of their strength, while others again looked as if they were making but their last feeble efforts at existence, though it was evident, from the heaps of consolidated geyserite surrounding them, that they had but recently passed through halcyon days of youthful energy and manhood power. Every here and there again we came upon others from whose wide open empty mouths came forth neither a puff of steam nor a drop of water. They were dead, and not a few of them were so completely eviscerated as to allow of the explorer to descend with perfect safety into the bowels of the earth through their vents. Geyser activity is in fact but the last act in the drama of volcanic life: all around proved this. Close at hand were stupendous cliffs of pure obsidian—the black bottle glass manufactured in Nature's furnaces. Even half a mile of our road was macadamised with it. And so similar not only in chemical composition but in optical properties is this obsidian to actual glass, that a flat piece I picked up on the road, just after it had been splintered off a block by one of the wheels of our carriage, is as transparent as any piece of black bottle glass of equal thickness. These mountains of obsidian plainly tell how awfully stupendous must have been the heating process which called them into existence, as well as how big must be the cavities left in the bowels[p. 162] of the earth from which the materials constituting them were obtained. No doubt water scoops out caverns in the softer strata composing the earth's crust, but these can scarcely be thought to equal in extent the cavities made by volcanoes. Think, for example, of what a hole in the earth must have been left by the 50 miles long and 5 miles broad lava stream which flowed from Mauna Loa in 1859, and fell as a fiery cascade over a cliff into the sea, in sufficient amount to fill up a large bay.
The geyser basin is in many places actually honeycombed with various sized caverns, either directly due to volcanic action, or to water, or to both combined, and these caverns, though widely apart, may yet freely communicate with each other by means of subterranean river courses. I have myself followed one river course into the bowels of the earth for three miles and more, in the great Adelsberg Grotto, in Styria. I have rowed across the lake in the dismally dark cavern at Han, in the Ardennes. And even in our own Derbyshire, I have seen, half-a-mile from the entrance of the Speedwell Mine, a river, a water-fall, and a lake, all of which tell that such natural phenomena exist within the bowels of the earth as well as upon its surface. Moreover, the resounding echoes from the clatter of our horses' feet as they briskly trotted over some of the geyserite, as well as the heat we experienced through the thick leather soles of our boots as we walked across it, was unmistakable proof that but a thin layer of crust separated[p. 163] the surface of the globe we were traversing in Wyoming and Montana not alone from vast caverns, but likewise from still active subterranean fires.
All the preceding facts I have narrated must be borne in mind, in order that the theory of geyser action I am now about to propound may be readily understood. For unless the reader believes:—
1st. That cavities of various shapes and sizes exist in the earth's crust;
2d. That the earth possesses internal lakes as well as rivers;