88 The Shoshone Island. 



If this seems an extraordinary depth for a 

 group of lakes one only need point out the 

 almost certainty that throughout the whole 

 time of this vast sedimentation the Cascade 

 mountains were subject to further uplifts, 

 and the depressions east and west of this line 

 of upfold were subject to correlated subsid- 

 ence, so that the earlier sediments of the Wil- 

 lamette valley on the west, and the beds of 

 these interior lakes on the eastward by their 

 gradual sinking, increase the capacity of these 

 depressions for continued sediments. 



This borne in mind, the depth of even three 

 thousand feet will not seem startling. 



Throughout this whole mass of lake sedi- 

 ments, fine and dense where it was deposited 

 in very deep and quiet water, fine sandstone 

 where the inflowing streams left the traces 

 of their emptying, all occasionally interstrati- 

 fied with beds of volcanic ashes, are inter- 

 spersed the leaves of plants, broken fragments 

 of wood, pieces of the bones of fish, of fowl, 

 or of mammal. 



