1 68 The Rocks of the John Day Valley. 



one of the finest life records of that remote 

 period, and with the record that volume, be- 

 coming at once the proximate cause of the 

 changes that followed, and the upper cover of 

 the volume it sealed. 



But this violent destruction of the life of 

 the period did not destroy that lake depres- 

 sion; it only partially filled its shallower por- 

 tions, and added thirty feet or more of sedi- 

 ment to the rest. The lake remained and still 

 continued to receive into its archives of hid- 

 den sediment tokens of the forces at work 

 among the hills around it. One remarkable 

 change marked that transition; the labora- 

 tories of the hills seem thereafter to have lost 

 the power to send forth from their secret re- 

 cesses heated vapors laden with mineral ma- 

 terials, as they had done, capable of changing 

 everything they touched to stone. The old 

 sediments of that lake, if originally clay, are 

 found changed to argillaceous rock; if sand, 

 changed to sand stone; if washed gravel, they 

 are found cemented into conglomerate. The 

 new sediments, if clay, remained clay; if sand, 



