56 
ALASKA GEOLOGY 
The curious tuff at Indian River, near Sitka, shows only 
andesite and basalt. 
The very interesting radiolarian chert of Halibut Cove, 
on Cook Inlet, which we compare with the Franciscan 
Series of California, of Jurassic or early Cretaceous age, 
has its own peculiar igneous rocks, crushed and altered 
spheroidal diabases and dacite-porphyries. 
At Dutch Harbor we studied the older beds of the 
newest series of volcanic rocks — highly altered augite- 
andesites — and through the Shumagin and Sannak islands 
and in the sea cliff sections on Hall and St. Matthew 
islands we were able to examine the whole series of these 
andesitic, trachytic, and basaltic rocks. We saw the 
newest of the series in the basaltic tuff cone at Black 
Bluff, on St. George Island, and in the wall of pearl-grey 
andesite on Bogoslof. 
