Hanna — Notes on Pribilof Islands. 221 



crack in the stratum permits the egress of one very large 

 spring and in the stream flowing from it fresh water 

 diatoms in pure gatherings can be had in great abun- 

 dance. The sand rock outcrops on toward Cascade Point 

 an unknown distance. As far as it has been traced it has 

 large numbers of springs flowing from it and it is under- 

 laid by massive igneous rock. On top there is the charac- 

 teristic lava in horizontal layers. 



The diatoms found in one small pocket were not well 

 preserved nor abundant but the species were all repre- 

 sented in the gatherings from Tolstoi Point, St. Paul 

 Island. 



Although these are the only known sedimentary 

 deposits on St. George Island it must be said that the 

 water line around Cascade Point and around the Big 

 Cliffs from Staraya Artel Rookery past Dalnoi Point and 

 to Zapadni Rookery has not been examined. 



Otter Island. 



The west end of this island has been elevated so that 

 about 75 feet or more of sandstone has been exposed. It 

 has not been carefully examined. On the opposite end of 

 the island may be seen an excellent crater which has been 

 cut into by the sea on one side. 



Age of the Islands. 



That the fossil-bearing sandstones were elevated at the 

 same time that the violent volcanic disturbances which 

 covered the islands with molten rock occurred seems cer- 

 tain from the fact that volcanic cinders are found in more 

 or less abundance in the topmost portions of the sedi- 

 mentary layers. If the age of the sand rock can, there- 

 fore, be accurately fixed this will determine the age of the 

 islands as they exist to-day to a fair degree of certainty 

 and this fact would be of value in the study of such ani- 

 mals as the fur seal. From the study of the mollusks 

 mentioned it seems to be post-Pliocene on St. Paul Island 

 and Pliocene on St. George Island. A study of the 

 diatoms indicates that the age of the two islands is the 

 same and that it is more apt to be Pliocene than a later 

 period. 



If the age of the Tolstoi Point (St. Paul Island) beds is 

 post-Pliocene it would be expected that the characteristic 



