218 Hanna — Notes on Pribilof Islands. 



Black Bluffs Exposure. 



For many years this was believed to be the only locality 

 on the Pribilof s where f ossiliferous rocks occnrred. The 

 first collections from it were made by a Russian natu- 

 ralist, Wossnessensky, in 1847-48. It appeared, to Dall 2 

 who summarized the information on the deposit up to 

 1896, that the early explorations yielded Miocene fossils 

 in a lime stratum. This had completely disappeared, 

 however, at the time of the Elliott investigations, 1872-74. 

 In the light of recent collections it seems somewhat doubt- 

 ful if Miocene fossils were ever found here and that possi- 

 bly some error in locality may have been made. 



Fortunately a good collection of shells has been made 

 from this exposure because the sea is fast tearing it away. 

 All the later gatherings were from nodules which were 

 water-worn and occurred in the layers of scoria at the 

 base of the cliffs. At the present time (1918) these are 

 exceedingly scarce. The sea has eroded the hill inward 

 beyond its crest and as the layers slope downward and 

 backward those at the base which contained the fossils 

 are beneath the sea. Since these nodules were detached 

 from the parent beds and thrown up by volcanic action 

 they do not represent the age of the layers in which they 

 were found, and it might be possible for fossils of more 

 than one age to have thus become mixed. Despite its 

 imperfections this exposure is very important because of 

 the study which it has received. A list of the mollusks 

 found has been published. (See bibliography.) 



Other Sedimentary Rocks. 



Besides the exposure just mentioned there are several 

 others on the islands where sandstones in situ outcrop. 

 These are as a rule near the surface of the sea and, as 

 stated above, are underlaid by massive green jasper. In 

 some places this was not sufficiently elevated to appear 

 above the water but the bowlders and pebbles which may 

 be seen on the beaches are indications here of the rocks 

 beneath the sand rocks. 



Ardiguen Rookery, St. Paul Island. — The sand rock at 

 this point extends from the water to a height of 15 or 20 

 feet. Above it there are lavas of about the same thick- 

 ness. All form a perpendicular cliff with loose rocks 

 piled at the bottom. The elevation has been caused by 



2 Seventeenth Annual Eeport U. S. Geological Survey, 1896. 



