688 THE ICE AGE IN NORTH AMERICA. 



cent activity of volcanic forces on the Pacific Coast, and of 

 the recency of the disappearance of the glaciers from the 

 mountains of the region. All competent observers have re- 

 marked the freshness of the lava deposits in the Snake river 

 Valley in Idaho, while Mr. Diller* has shown that in the 

 great interior basin in California near Lassen Peak, between 

 Snag Lake and Lake Bidwell, there is a region many miles in 

 extent covered with lava and volcanic ash to a uniform depth 

 of many feet, with cones rising more than 600 feet, all of which 

 must have been ejected within the last 200 years. Stumps 

 of trees are still projecting from the stratum of volcanic ash 

 which killed them, while the charred trunks of other trees 

 which were overwhelmed by the lava stream still remain 

 undecayed. It is impossible that these trunks could have 

 resisted the corroding agencies even of this dry atmosphere 

 for many centuries while none of the fresh trees growing on the 

 surface of the stratum of volcanic ash are more that 200 years 

 old. 



It should be remembered also that the vast erosion since 

 the auriferou gravels were covered by lava was hastened by 

 the enormous floods which occurred when the glaciers which 

 had been subsequently formed melted off. The floods aris- 

 ing from the annual melting of the snow in the region are now 

 enormous. How much greater must they have been in the 

 declining years of the Glacial Epoch! 



The first evidence upon the point to which we will turn 

 attention is that produced by Professor J. D. Whitney t of 

 Harvard University, concerning human remains believed by 

 him to have been found in strata which mark the closing 

 period of the Tertiary epoch in California. 



The following description of the deep placer deposits in 

 which these remains have been found is given by Le Conte: 



* See "Bulletin of U. S. Geol. Survey/' No. 79, 1891. 



f "Report on the Auriferous Gravels of the Sierra Nevada," 1879, 

 p. 258 et seq. 



