LOWER JURASSIC 397 



species of Pecten, Pinna, and two or three species of Ammonites repre- 

 sented by fragmentary specimens, one of which seems to be an Arietites 

 or a closely related form. The Myophoria (?) is a small shell with four 

 strong radiating ribs, and if the genus is correctly determined it would 

 suggest an age as old as the Rhetic, but the other fossils give stronger 

 evidence of Jurassic age. None of the fossils in this little assemblage is 

 known elsewhere in Alaska, and we are unable to make any definite cor- 

 relation with other American formations, although rocks of the same age 

 doubtless occur in the California section. 



It is probable that Lower Jurassic rocks of a different character occur 

 on the Alaska peninsula. At Cold bay there are nearly 4,000 feet of 

 shales and sandstones lying between the determined Triassic rocks and 

 the Cadoceras-bearing Enochkin formation, but their exact position in 

 the Jurassic or Triassic was not determined by paleontologic evidence. 

 In the Cold Bay section the unconformity between the Triassic and the 

 Jurassic is not so obvious as at some other localities, and the boundary 

 between the two systems was not definitely fixed by our very limited 

 examination, the relations being obscured by several important faults 

 and by the absence of characteristic fossils in the critical part of the 

 section. It is more than probable, however, that there is an unconform- 

 ity above the Triassic. The Ammonites from Kialagvik or Wide bay 

 described by White are referred by Pompeckj to the Upper Lias, and 

 Hyatt referred other collections from the same bay to the base of the 

 Lower Oolite, stating that they are related to faunas that are called 

 Upper Lias by German geologists. These are in unaltered sandstones, 

 and whatever may be the final decision as to their age, they are evidently 

 older than any part of the Enochkin formation. Hyatt also tentatively 

 referred certain specimens of Lytoceras and Phylloceras from Kamishak 

 bay to the Upper Lias, but we now know that they really come from the 

 Upper Jurassic Aucella beds of the Naknek formation. 



The Yakutat formation, on Kodiak island, across Shelikof strait from 

 the Alaska peninsula, which was referred to the Lower Jurassic by 

 Ulrich, differs completely in both lithologic and paleontologic features 

 from all the Jurassic formations known in the region, and as the fossils 

 it has yielded are all new forms of doubtful affinities, its exact age is 

 still uncertain. 



MIDDLE JURASSIC— ENOCHKIN FORMATION 



The Enochkin formation is typically exposed on the east shore of 

 Enochkin bay, from which it was named.* It extends from here in a 



*The petroleum fields of the Pacific coast of Alaska, with an account of the Bering River coal 

 deposits. Bull. 200, U. S. Geol. Survey, 1904, pp. 37-55. 



