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falling upon the gradually cooling rock, were no longer converted into 

 steam and thrown back into the air, only to condense and fall again, but 

 being able to remain in liquid form upon the rock, sought lower levels, 

 and thus new streams began to flow. The rhyolite, obsidian, and trachyte 

 were very hard and eroded slowly, but when the streams reached the edge 

 of the lava-held they encountered rock which was comparatively soft and 

 which wore away rapidly. The result is that every stream leaving the 

 Yellowstone Park has one or more great waterfalls in its course where it 

 leaves the lava-sheet. Notably among these streams are Lewis River, the 

 outlet of Lewis and Shoshone lakes, Yellowstone River, the outlet of 

 Yellowstone Lake, Gardiner, Gibbon, and Firehole rivers, and Lava, 

 Lupin, Glen, Crawfish, Tower and Cascade creeks, all leaving the lava- 

 sheet in beautiful falls, varying from 30 feet to over 300 feet in vertical 

 descent. With scarcely an exception, all these streams and lakes are of 

 the best of pure, clear, cold water, well supplied with insect larva?, the 

 smaller Crustacea, and various other kinds of the smaller animal and plant 

 forms sufficient in amount to -support an immense fish-life. But it is a 

 strange and interesting fact that, with the exception of Yellowstone Lake 

 and River, these waters were wholly barren of fish-life. The river and 

 lake just named are well filled with the Rocky Mountain trout (Salmo 

 myhm), and this fact is the more remarkable when it is remembered that 

 the falls in the lower Yellowstone River are 109 and 308 feet, respectively, 

 by far the greatest found in the Park. 



The total absence of fish in Lewis and Shoshone lakes and the numerous 

 other small lakes and streams of the Park is certainly due to the various 

 falls in their lower courses which have proved impassable barriers to the 

 ascent of fishes from below; for in every one of these streams just below 

 the falls trout and, in some cases, other species are found in abundance. 

 But to account for the presence of trout in Yellowstone Lake was a matter 

 of no little difficulty. If a fall of 30 to 50 feet in Lewis River has prevented 

 trout from ascending to Lewis and Shoshone lakes, why have not the 

 much greater falls in the Yellowstone proved a barrier to the ascent of 

 trout to Yellowstone Lake? Certainly, no fish can ascend these falls and 

 we must look elsewhere for the explanation. 



Many years ago the famous old guide, Jim Bridger, told his incredulous 

 friends that he had found on the divide west of the L T pper Yellowstone 

 a creek which flowed in both directions— one end flowing east into the 

 Yellowstone, the other west into Snake River. But as he also told them 



