636 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



beds. Near Coal Creek the Aucella-bearing beds seem to underlie the Upper Carboniferous 

 limestone, which has apparently been thrust over them. 



E 3. CAPE LISBTJRNE, NORTHWESTERN ALASKA. 



Collier ^®^° found a thick sequence of strata apparently overlying the Corwin 

 formation (Jurassic), and in the absence of fossils assigned it provisionally to the 

 Lower Cretaceous. He describes it as follows: 



Southwest of the area occupied by the Corwin formation, and lying between it and the 

 Carboniferous rocks exposed at Cape Lisburne, there is a series of beds which, though they 

 resemble the Corwin Jurassic rocks, are easily differentiated from them on lithologic grounds. 

 These rocks outcrop along the coast from a point 2 miles west of Corwin Bluff to within 3 miles 

 of Cape Lisburne and extend inland in a southeasterly direction. * * * * The exact contact 

 of this formation with the Corwin was not exposed, or if observed its significance was not 

 understood, though the field relations of the two formations are definitely known at a number 

 of localities. Continuous sedimentation and conformity between the formations are indicated, 

 though the possibility of thrust faulting along the contact should not be overlooked. This 

 formation is therefore provisionally regarded as overlying the Corwin and constituting an upper 

 member of the Mesozoic series. * * * 



LithologicaUy this formation consists of sandstones and shales, with the former in the 

 ascendant. The sandstone beds range in thickness from a few inches to 20 or more feet. They 

 resemble the sandstones of the Corwin formation, but taken as a whole are probably somewhat 

 less gritty and contain no conglomeratic material. The shales which are interbedded with the 

 sandstones are dark colored and sometimes micaceous, so that they have a silvery sheen on the 

 bedding faces. In a few instances ripple marking was observed on shaly beds. 



No definite fossils were found, after a diligent search, either in the sandstones or the shales, 

 though indistinct impressions of vegetable fragments, probably detrital material, were found 

 in some of the beds. The structure of the formation, while it consists of simple open folds near 

 its boundary with the Corwin, becomes increasingly complicated as the fault at the contact 

 with the Carboniferous rocks is approached. Overturned folds and minor thrust faults with 

 axes extending in a general way northwest and southeast are typical features. * * * 



Owing to the complex structure of this formation, it was impossible to definitely measure 



its thickness, but from the imperfect evidence obtained it is believed to be not less than 5,000 



nor more than 15,000 fee't, and for the purposes of this report it is estimated at 10,000 feet. 



Since no direct paleontologic or paleobotanic evidence was obtained, the age of the formation 



can only be inferred from its relation to the Jurassic Corwin formation, which it overlies. It 



is therefore provisionally assigned to the Lower Cretaceous. On Anaktuvuk River, 400 miles 



east of Cape Lisburne, Schrader found a formation somewhat similar to this, both in its lith- 



ology and in its topographic relations to the Lisburne formation, which he called the Anaktuvuk 



series " and which contains Lower Cretaceous fossils. If the above assignment is correct, the 



upper Mesozoic formation of the Cape Lisburne region should be correlated with the Anaktuvuk 



series. 



R 5. NORTHERN ALASKA, ARCTIC SLOPE. 



According to Schrader ^°^ ' the Cretaceous which he crossed in descending the 

 Colville may be divided into two groups, which are unconformable — "the Anak- 

 tuvuk (Lower Cretaceous) and the Naniishuk series (Upper Cretaceous)." 



The Anaktuvuk is made up of fine, heavy-bedded sandstones, or arkose — sometimes a 

 grit, with little conglomerate — the whole aggregating at least 2,000 feet. Resting unconform- 

 ably on these are sandstone, impure limestone, slate, quartzite, and chert, which make up the 

 Nanushuk series. The Anaktuvuk carries Aucella crassicolis Keyserling, making it Jura- 

 Cretaceous, wMle the Nanushuk has yielded Upper Cretaceous fossils. The Nanushuk, like 

 the Upper Cretaceous of the lower Yukon, contains coal seams of excellent quality. 



o Schrader, F. C, Reconnaissance in northern Alaska: Prof. Paper U. S. Geol. Siu-vey No. 20, 1904, pp. 74-76. 



