EARLIER TERTIARY (EOCENE AND OLIGOCENE). 791 



overlying gravels at the localities where their relations to the underlying deposits were observed, 

 whether ia horizontal or tilted strata, were found to be structurally conformable. They are 

 characterized by a yeUow color. They include both fine and coarse material, are well worn 

 and well rounded, and the predominant constituents are white quartz and chert of various 

 colors, principally black. There is a considerable proportion of metamorphic rocks and many 

 pebbles of compact chert conglomerate. In the upper part of the gravels, in strong contrast 

 with their medium to fine grained material, are locally many bowlders of granitic rocks and 

 diabase and a few well-rounded bowlders of dense chert and quartzite conglomerates. The 

 greatest observed thickness of these deposits was approximately 3,500 feet. The upper gravels 

 constitute about half of the entire deposit. 



FossU leaves are observable nearly everywhere ia the beds associated with the coal, but 

 except where these beds have been baked by the burning of the coal the fossils are poorly 

 preserved. The age of the coal-beariag member has been determined as Kenai. The age of 

 the gravels has not been determined, nor is it definitely known that they are chronologically 

 conformable with the underlying deposits, but they have been folded at every point where 

 folding was observed, along with the underlying deposits. Where valleys have been extensively 

 developed in these deposits bench gravels have in many places been laid down on the truncated 

 edges of the older deposits, and where these older beds are horizontal the bench gravels are 

 in apparent conformity with them, obscuring the relationship. It is probable that deposits 

 of various ages since the Kenai, formed under varied conditions of sedimentation, occur in this 

 area and that the coarse material in the uppermost part of the gravels owes its origin to 

 glaciation. 



Parts of the gravel members of these deposits are auriferous and have suppUed the gold 

 for the Bonnifield region. There is a marked resemblance between these coal-bearing deposits, 

 with their thick beds of overlying gravels, and the Kenai beds of the SeventypiUe Creek area 

 near Eagle, with their coal-bearing deposits and thick beds of conglomerate, formed largely 

 of the same kinds of material. 



Q 3. SEWARD PENINSTJIiA. 



Moffit/^* in his report on the Fairhaven gold placers, states that "In the north- 

 eastern part of Seward Peninsula Ugnitic coal has 'been mined in a small basin on 

 Kugruk River. The associated strata are sandy and shaly and include thin lime- 

 stones. Though folded and jointed, they are less metamorphosed than the neigh- 

 boring schists. No fossils have been found and the age is indeterminate," but the 

 rocks are presumably late Cretaceous or early Tertiary. The area is too smaU to 

 be shown on the map of North America. 



Q 3-4. NORTON SOUND. 



MendenhaU ^^ mentions the occurrence of coal-bearing strata supposed to be 

 of Tertiary age outcropping on Tubutulik and Koyuk rivers. 



a 4-5. KOBTTK RIVER. 



Strata belonging to the early Tertiary were found by MendenhaU ^ on Kobuk 

 (Kowak) River and also farther east on Dall River, in separate local basins. They 

 comprise conglomerates, of quartz pebbles with some pebbles of the neighboring 

 crystalline rocks, soft sandstones, shales, and lignite beds. On the basis of fom- 

 recognized species of plants Knowlton referred the strata to the "Arctic Miocene" 

 (upper Eocene) . 



