38 PETROLEUM OE PACIFIC COAST OF ALASKA. [bull. 250. 
Tilted Hills. The formations lie in belts parallel to the coast. The 
relation of the sedimentaries to the crystallines is complex and 
obscure, but the remainder of the series is conformable throughout 
(except for an unconformity between the Jurassic and the Tertiary) 
and is gently and simply folded. The general section is as follows: 
General section of the Cook Inlet petroleum fields. 
Tertiary : Feet. 
Sandstone, shale, and conglomerate with fossil trees and leaves 100? 
Upper Jurassic: 
Naknek formation: Interhedded sediments and volcanic rocks (ar- 
kose, andesite, tuff, sandstone, and shale) 5,000 
Agglomerate (best developed on Enochkin Bay) 300 
Middle Jurassic: 
Enochkin formation (shale and sandstone with some conglomerate)- 3,000? 
Pre-Jurassic : 
Coarse crystalline rocks. 
PRE-JURASSIC CRYSTALLINES AND INTRUSIVES. 
The crystalline rocks of the Chigmit Mountains extend along the 
entire western shore of Enochkin Bay and both shores of the northern 
arm of that bay. There is considerable variety in the series, but 
granite and rocks similar in texture and general appearance pre- 
dominate. 
The exposures along the eastern margin of this belt consist of 
basalts varying considerably in appearance. The eastern side of the 
point between the arms of Enochkin Bay contains good exposures oi 
a reddish porphyritic rock. A greenish rock is exposed east of this 
on the northern shore of the eastern arm of the ba}', and a rock o 
similar color and appearance is exposed on the north shore of Chi 
nitna Bay. These rocks were shown by microscopic study to be o »j 
identical mineralogic composition, and were determined to be basal 
The basalt may be either a member of the pre-Jurassic crystallir 
complex which forms the main mass of the Chigmit Mountains an 
the backbone of the Alaska Peninsula, or a post-Jurassic intrusiv 
The writer is inclined toward the former view. 
MIDDLE JURASSIC ROCKS. 
Enochkin formation. — The rocks overlying the crystallines cons 
of a thin conglomerate at the base, followed by more than 3,000 f< 
of dark sandy shales with occasional bands of sandstone, conglom 
ate, and limestone and many fossil beds; they are well exposed in i 
cliffs on the east shore of Enochkin Bay. Rocks of the same lit 
logic character extend along the strike northward from these ex f- 
sures, passing the heads of Oil and Dry bays to Chinitna Bay. T 
have not been followed by the writer beyond the north shore |f 
