PRIBILOF ISLANDS. 131 



Stanley-Brown found the islands to be entirely volcanic, and for the 

 most part basaltic. The centers of eruption are still recognizable, and 

 the date of origin of the accumulations is regarded as post- Pliocene. No 

 erratics are found upon the higher levels and there are no traces of gla- 

 ciation either general or local.* Raised beaches were not observed, except 

 in one instance which is believed to be due to local volcanic disturbance. 

 The island of Saint George has been consideraly affected by orographic 

 movement since its formation, but that of Saint Paul is believed to have 

 remained unchanged. 



Though several visits were made to these islands during the summer 

 of 1891, my opportunities for geological observations there were very 

 small as compared with those of Mr Stanley-Brown and the facts noted 

 therefore require the briefest mention only. 



The most interesting locality on either island is undoubtedly that of 

 Black bluff, Saint Paul island, where fossils have been collected by 

 Wassressenski, Elliott and others as well as by Mr Stanley-Brown. I 

 had the pleasure of visiting this place with the last named gentleman, 

 and entirely concur with his view as to the mode of occurrence of the 

 fossils, namely, that they are found only in detached fragments of cal- 

 careous argillite which are included in a deposit of basaltic scoria and 

 volcanic ash.* The distinctly bedded character of this enclosing rock, 

 however, leads me to believe that it was laid down under water, the 

 products of the volcanic eruption being there mingled with fragments 

 ripped up from the sea-bed by the same force. If this view be correct, 

 it follows that the island, or this part of it at least, has been elevated by 

 an amount of at least 80 feet since the time of the eruption. 



The manner in which the fossils occur at this place shows that they 

 cannot be accepted as fixing the ])recise age of the formation, but only 

 as representing some beds which already existed at that time. Thus 

 the fact that all the molluscs collected here by Mr Stanley-Brown are 

 still living species, while earlier collections included some species now 

 extinct, presents no difficulty. t It tends merely to show that deposits 

 due to the upper Miocene (Astoria group of Dall), with others to which 

 a post-Pliocene date must be attributed, occur in the bed of this part 

 of Bering sea, and to confirm the later post-Pliocene date accorded 

 to eruptions which have produced the islands. 



Another fact which seems to show that the island of Saint Paul must 

 have been upraised to some extent since the date of the period of vul- 

 canism is the difference of contour which exists between the higher hills 

 of the island and the sometimes widely extended lower slopes attaching 



* Op. cit., p. 497. 



fOp. cit., p. 498. Bull. U. S. Geol. Survey, no. 84, pp. 257, 258. 



