32 ALASKA GEOLOGY 



J. Stanley-Brown, to whose full geological description of 

 the island L we were not able to add, kindly gave us several 

 large blocks of the highly fossiliferous post-Pliocene rocks 

 which are found in the coarse basaltic tuff of which the 

 Black Bluff is made. These included fragments are 

 rounded, and are charged with bivalve shells, mainly Car- 

 dium, which make up nearly half the mass. The rock is 

 a firmly indurated marly clay, and yet since our specimens 

 were brought away they have fallen asunder into a great 

 number of pieces. The rock has been described by Dr. 

 Dall, 2 who reports that all the shells are still found in the 

 neighboring sea. 



Several slides of the basalts of St. Paul were examined. 

 One (157) is a glassy amygdaloidal basalt containing 

 augite, olivine and plagioclase in well-defined porphyritic 

 crystals in a black granulated glassy base. This is the 

 ' newer scoriaceous lava ' of Mr. Stanley-Brown. 



The < older ' rock of Stanley-Brown (151) is a finely mi- 

 arolitic, very olivinitic basalt of the Meissen type, with 

 large red olivines, pink augite, plagioclase and magnetite, 

 in a glassy base. 



A third type of basalt was collected at the landing, 

 from near the base of the Black Bluff cinder cone. It is 

 intermediate in color between the others, more compact, 

 but full of very large steam holes. The abundant olivine 

 is in very fine, large, skeleton crystals, in a glassy base 

 containing much magnetite and augite. 



ST. MATTHEW ISLAND 



A third of the way north across Bering Sea, from Una- 

 laska, is the Pribilof group of which we have just spoken. 

 A third farther north are St. Matthew and Hall islands. 



1 Geology of the Pribilof Islands, Bull. Geol. Soc. Am., vol. in, p. 496. 

 1892. See also Dr. Geo. M. Dawson, Geological Notes on Bering Sea, etc., Bull. 

 Geol. Soc. Am., vol. v. p. 130. 1894. 



8 Bull. 84, U. S. Geol. Survey, p. 255. 1892. 



