176 THE POPULAR SCIENCE MONTHLY. 



It has been my good fortune to make explorations in Montana, 

 Wyoming, Idaho, and the Yellowstone Park which have cleared 

 up some of these difficulties. The presence of trout in Yellow- 

 stone Lake and the total absence of all fish from the other large 

 lakes of the park was one of the most interesting of these anom- 

 alies, and it is to its explanation that this article is devoted. 



It is certain that all the streams and lakes of the territory 

 covered by the lava flow were wiped out of existence by the fiery 

 flood, and all terrestrial and aquatic life destroyed. Many long 

 years must have passed before this lava sheet became sufficiently 

 cooled to permit the formation of new streams ; but a time finally 

 came when the rains, 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. And then the fishes in the con- 

 necting streams below, which had not been destroyed by the 

 lava flow, began to invade the desolated region and repeople its 

 waters. 



The rhyolite, obsidian, and trachyte were very hard and eroded 

 slowly, but when the streams reached the edge of the lava field 

 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. Notable among these streams are 

 Lewis River, the outlet of Lewis and Shoshone Lakes ; Yellow- 

 stone River, the outlet of Yellowstone Lake ; Gardiner, Gibbon, 

 and Firehole Rivers, and Lava, Lupine, Glen, Crawfish, Tower, 

 and Cascade Creeks, all leaving the lava sheet in beautiful falls, 

 varying from thirty feet to over three hundred feet in vertical 

 descent. The following is a list of the principal waterfalls in the 

 streams in and about the park, each one of which is supposed to 

 form an insurmountable barrier to the ascent of fish : 



Great Falls of the Yellowstone 308 feet. 



Upper Falls of the Yellowstone 109 " 



Crystal Falls in Cascade Creek 129 " 



Tower Falls in Tower Creek 132 " 



Undine Falls in Lava Creek 60 " 



Lower Falls in Lava Creek 50 " 



Wraith Falls in Lupine Creek 100 " 



Osprey Falls in Gardiner River , 150 " 



Rustic Falls in Glen Creek 70 " 



Virginia Cascades in Gibbon River 60 " 



Gibbon Falls in Gibbon River 80 " 



Keppler Cascade in Firehole River 80 " 



Upper Falls in Lewis River 50 " 



Lower Falls in Lewis River 30 " 



Moose Falls in Crawfish Creek 30 " 



