194 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



sea level. A sharp contrast is seen between the steep rounded slopes of 

 the sandstone and the irregular outline of rhyolite. The latter is marked 

 by long, narrow drainage channels, with steep bluffs on the west side, 

 parallel to the valley of Heart River. These bluffs stand out from 20 to 

 50 feet above the depression. The intervening ravines are the result of 

 ice movements and are occupied by small ponds and meadows carved out 

 of glacial drift, 



OUTLET CANYON. 



This impressive gorge cuts a deej:>, broad passage completely through 

 Chicken Ridge. In the strict use of the word it is a true canyon, quite 

 unlike any other canyon or drainage channel in this part of the country, 

 and is one of the most interesting geological features to be found within the 

 Park. It affords an instructive section across the range from Grouse Creek 

 to Heart River, with the Montana sandstones constituting the center of the 

 ridge, flanked on both sides by rhyolite hills. Overlook and Channel 

 mountains, on opposite sides of the canyon, form a part of the same mono- 

 clinal uplift, the strata striking with the ridge. 



The interesting feature about Outlet Canyon is that it at one time 

 served as the discharge for the waters of Yellowstone Lake. This ma°'- 

 niheent sheet of water, which now flows northward and drains to the 

 Atlantic through the famous Yellowstone Canyon, formerly discharged 

 by way of the south arm through Outlet Canyon to Snake River and 

 thence onward to the Pacific. The discovery of Outlet Canyon as an 

 ancient drainage channel for Yellowstone Lake was made by the writer in 

 1889. For several years he had been firmly convinced, by geological 

 reasoning that seemed unanswerable, that this grand lake at one time 

 must have discharged southward, and consequently into the Pacific. All 

 attempts to locate such outlet proved futile till the autumn of that year. 

 It Avas hidden by dense forests, obscured by glacial drift, and abandoned 

 as a waterway. After the discovery of this old and neglected channel all 

 fresh observations tended to strengthen and confirm the arguments that the 

 lake formerly found its outlet to the south. In the chapters treating of 

 the physiographic features of the Park, in Part I of this monograph, the 

 problems connected with the ancient drainage of Yellowstone Lake are 

 discussed at some length and Outlet Canyon is described in detail in its 



