In those distant days the altitude of this region was not great, nor was the ocean as remote from its borders as now. The forces which already had lifted considerable areas above the sea and fashioned them into an embryo continent were still at work. The earth-shell, yet soft and plastic, was not strong enough to resist the double strain caused by its cooling, shrinking outer crust and the expanding, molten interior. Volcanic eruptions, magnificent in extent, resulted and continued at intervals throughout the Pliocene period. These eruptions were accompanied by prodigious outpours of lava that altered the topography of the entire mountain section. Nowhere else in all creation has such an amount of matter been forced up from the interior of the earth to flow in red-hot rivers to the distant seas as in the western part of the United States. What a panorama of flame it was, and what a sublime impression it must have made on the minds of the primeval men who witnessed it from afar as they paddled their canoes over the troubled waters that reflected the red-litten heavens beneath them! Is it remarkable that the geyser region of the Park is a place of evil repute among the savages and a thing to be passed by on the other side, even to the present day?
[Illustration: _Detail from Jupiter Terrace_]
When the elemental forces subsided the waters were fishless, and all aquatic life had been destroyed in the creation of the glories of the Park and its surroundings. Streams that once had their origins in sluggish, lily-laden lagoons, now took their sources from the lofty continental plateaus. In reaching the lower levels these streams, in most instances, fell over cataracts so high as to be impassable to fish, thus precluding their being restocked by natural processes. From this cause the upper Gardiner, the Gibbon and the Firehole rivers and their tributaries--streams oftenest seen by the tourist--were found to contain no trout when man entered upon the scene. From a sportsman's viewpoint the troutless condition of the very choicest waters was fortunate, as it left them free for the planting of such varieties as are best adapted to the food and character of each stream.
The blob or miller's thumb existed in the Gibbon river, and perhaps in other streams, above the falls. Its presence in such places is due to its ability to ascend very precipitous water courses by means of the filamentous algae which usually border such torrents. I once discovered specimens of this odd fish in the algous growth covering the rocky face of the falls of the Des Chutes river, at Tumwater, in the state of Washington, and there is little doubt that they do ascend nearly vertical walls where the conditions are favorable.