1881. ] Glacial Phenomena in the Yellowstone Park. 207 
That a very profound erosion had taken place along the course 
of the cafion at a very early date is proved by the fact that during 
the rhyolitic period as well as the basaltic and andesitic, there 
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: Glacial Phenomena of the Yellowstone Park. 
were cafions almost as deep as the present one, into which the 
coulées cascaded. At one spot near the northern base of Mt. 
Washburn the section of a fossil river is exposed, more than 
