CHAPTER X. 



LIFE OF SURFACE DEPOSITS. 

 SURFACE BEDS. 



The field intended by the term Surface 

 beds includes all slight depressions of the sur- 

 face producing ponds with sediment enough 

 to preserve bones and teeth washed into them, 

 and also swamps and bogs into which large 

 mammals often sink to their death, leaving 

 their bones to such preserving agencies as 

 might occur there. And inasmuch as the lat- 

 est great surface leveling agency of the north 

 temperate zone was that of the glacial ice, 

 most of these surface depressions would date 

 from glacial times, and would, therefore, be 

 properly designated as Pleistocene. Further- 

 more, up to the glacial period the horse and 

 the camel were abundant here, and the ques- 

 tion of their continuance in Oregon through 

 glacial times is still in doubt, so that our 

 group of surface sediments must provide the 

 settling testimony on this question. 



