SMITHSONIAN EXPLORATION IN ALASKA 



Photo, by Collier. 



I. Palisades on the Yukon River thirty miles below the mouth of the Tanana 

 River, showing blocks of frozen silts as they are undermined and subside into 

 the river. 



Photo, by Collier. 



2. Pleistocene Silt Blutt on the Klalishkakat, a tributary of the Yukon, 

 showing a mammoth tusk protruding from the bank. 



