3 2 
ALASKA GEOLOGY 
J. Stanley-Brown, to whose full geological description of 
the island 1 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 - 
diuMj 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. 
Dali, 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 
6 newer scoriaceous lava’ of Mr. Stanley-Brown. 
The 6 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. hi, p. 496. 
1892. See also Dr. Geo. M. Dawson, Geological Notes on Bering Sea, etc., Bull. 
Geol. Soc. Am., vol. v, p. 130. 1894. 
2 Bull. 84, U. S. Geol. Survey, p. 255. 1892. 
