2 6 
ALASKA GEOLOGY 
mainland, and to the southwest through the double line 
of islands on the west side of Prince William Sound. It 
is probable that they are older than, and occupy the axis 
of an anticline in, the Vancouver Series. 
COOK INLET 
Mr. Palache landed at Halibut Cove, in Kachemak Bay, 
Cook Inlet, and found an interesting section of green and 
red radiolarian cherts, in thin and very regular beds sepa¬ 
rated by clay or shale partings, beautifully folded and con¬ 
torted (plate ix). With them are associated intrusive masses 
of diabase, much crushed and altered, showing in places a 
distinct spheroidal structure, the surfaces of the spheroids 
being largely covered with minute spherulites. Small 
amounts of sandstone and conglomerate are also present. 
The series is cut by a group of conspicuous light-col¬ 
ored porphyry dikes, standing nearly vertical, parallel, and 
20, io, 50 and 60 feet in width, respectively. Under the 
microscope these dike rocks proved to be much altered 
dacite-porphyries, showing phenocrysts of embayed 
quartz, acid plagioclase much altered to calcite and kao¬ 
lin, and occasional orthoclase in a granular to granophy- 
ric groundmass of quartz and feldspar. Chlorite is spar- 
ingly present throughout the rock, but the bisilicate from 
which it was derived could not be determined. The 
dikes are quite coarsely porphyritic near their centres, but 
toward the contact with the cherts become almost aphan- 
itic. The cherts are whitened for a few inches from the 
contact but not otherwise altered. 
With the exception of the dike rocks, this section bears 
an altogether extraordinary similarity in structure and 
lithologic character to the radiolarian cherts and associ¬ 
ated igneous and clastic rocks of the Franciscan Series 
of the California Coast Range, especially well developed 
on the San Francisco Peninsula. These have been de- 
