3oo 



University of California. 



[Vol. 2. 



As has previously been stated, the John Day is largely made 

 up of volcanic ash and tuff, which does not appear to have suffered 

 much from working over. Sands, gravels, and muds, such as 

 belong to characteristic lake beds, are confined to the top of the 

 series. While molluscan remains are quite common at many hori- 

 zons, fresh-water forms are known only in the sands and gravels 

 mentioned above. The numerous molluscan shells, found in the 

 ash and tuff beds, are of land forms. Plant remains, also, which 

 characterize lake beds are, excepting some petrified wood, confined 

 to the highest strata. A solitary leaf, found many years ago in 

 the middle stage at Turtle Cove, is the only known exception to 

 this rule. Fish remains have not been found at all in this series. 

 Tortoise bones are very abundant, but so far the writer has not 

 learned of the existence of any water forms of this order. The 

 only aquatic mammalia which have been found are rodents. 

 Remains belonging to members of the beaver family seem to occur 

 at several horizons through the section. In short, while organic 

 remains are abundant in the greater portion of the John Day, 

 aquatic forms are found only in limited sections of the series. 

 One could account for the absence of water forms by supposing 

 the lake to have been salt or alkaline, though there does not appear 

 to be any definite evidence in support of this view. 



An objection to the lacustrine hypothesis as applied to the 

 ashy beds is found in the fact that, while the greater part of the 

 deposit is composed of fine material, large, isolated mammalian 

 bones are scattered all through it and over wide areas of the same 

 horizon. Many of these bones are evidently parts of skeletons 

 which were torn apart and scattered about on a land surface before 

 they were finally buried. If they were carried out into a lake it is 

 hard to understand how they could be selected for distribution in 

 deposits from which all other large fragments of detrital material 

 are absent. Occasionally carcasses might be floated out into a 

 lake and finally buried in fine deep-water deposits. In such cases 

 many, if not all, of the bones would be found together. The pres- 

 ence of a considerable portion of the fossil material could not be 

 accounted for in this way. 



A possible explanation of these occurrences is that a shallow 



