The Rocks of the John Day Valley. 173 



period, and a continued lake depression sur- 

 rounded by elevated ridges of hills, rising in 

 many places into mountain magnitude, im- 

 plies the deposit of continued sediment, and 

 this necessarily becomes the page upon which 

 the history of the life along its shores is writ- 

 ten. The winds would always blow into the 

 waters of the lake their burden of leaves, and 

 the floods of winter wash there some frag- 

 ments of the bones of the animals that char- 

 acterized the period. It must have happened, 

 then, that at the close of each great period as 

 indicated here, the animal life of these ancient 

 lake shores was entirely destroyed by fire, 

 flood and the poisonous vapors that tainted 

 earth, air and waters, or else those to whom 

 migration was possible escaped to some other 

 region. The supposition of their entire de- 

 struction encounters this difficulty: the de- 

 struction of the entire fauna of Oregon, and 

 even of the whole western slope of the conti- 

 nent, would not have secured the results ob- 

 served, unless we suppose a like destruction 

 extending to the Atlantic coast; for the same 



