MARTIN.] 
GEOLOGY OF COOK INLET REGION. 
45 
shales are well exposed on the southern shore and near the mouth 
of Chinitna Bay. From this point, along Cook Inlet to Oil Bay, a 
continuous section of the series of flows is to be seen, the total thick- 
ness of which has not been measured, but is probably about 3,500 
feet. The igneous rock is occasionally interbedded with shales, which 
in the cliffs between Oil Bay and Dry Bay contained Belemnites. 
They are thus shown to be of Mesozoic age. Probably the igneous 
rocks with their interbedded shales are to be referred to the upper 
Jurassic. This series is certainly allied in age and is the equivalent 
of the Naknek formation which Spun* b described from the shores of 
Naknek Lake. It would appear from Spurr's description of this for- 
mation, as well as from the writer's observations, that it contains 
more arkosic material and less fine, well-assorted sediments than the 
shales of the Enochkin formation. Enough fossils have been col- 
lected from the Naknek formation to determine from paleontologic 
Fig. 3. — Enochkin formation, capped by Naknek formation, Oil Bay. 
evidence the exact faunal equivalency. It seems best, therefore, in 
view of the lithologic similarity and the relations of the faunas, to 
use the same for the rocks exposed on the western shore of Cook Inlet. 
POST-JURASSIC ROCKS. 
North of the mouth of Chinitna Bay is a belt of lowland which 
extends eastward for several miles. The shore consists of alternate 
bluffs and beaches, the latter thrown across the ends of swamps and 
one or two forming lagoons behind them. A number of the bluffs are 
"Abundant fossils, including AuceUa and other characteristic upper Jurassic forms, 
were collected from these beds during the summer of 1904. Doctor Stanton considers 
the evidence of these fossils sufficient both for the reference of these beds to the upper 
Jurassic and for correlation with the Naknek formal ion of (lie Alaska Peninsula region. 
b Spurr, J. E., A reconnaissance of southwestern Alaska : Twentieth Ann. Rept. U. S. 
Geol. Survey, pt. 7, 1900, pp. 169-171. 
Bull. 250—05 M 4 
