578 



CLARENCE N. FENNER 



suggestion seemed from the first to have decided merits and later 

 investigations served to strengthen it. Moreover, as evidence of 

 various kinds accumulated, a much more complete conception of 

 the attendant processes was afforded. 



The make-up of the deposit itself, its situation with respect to 

 the configuration of the landscape, and various striking effects 

 produced by it demand that certain definite characteristics should 

 be attributed to it at the time of its appearance, and prescribe 



Fig. 7. — Looking northerly down the Valley of Ten Thousand Smokes. Photo- 

 graph by R. F. Griggs, 1917. 



rather rigid limitations to one's ideas as to its possible derivation. 

 Observations show plainly that, in the first place, this material 

 was not thrown violently into the air to descend over the general 

 landscape, but that it was restricted very definitely to topographic 

 depressions. In point of time, it was one of the first manifestations 

 of activity, for it is covered by the subsequent ash-falls. The 

 thorough manner in which vegetable material engulfed by it was 

 carbonized and the indications of brush fires started by it can 

 "hardly be explained except on the supposition that it possessed a 

 high temperature, probably near incandescence. In many places 



