MESOZOIC BOCKS, NANUSHUK SERIES. 79 



coal-bearing Upper Cretaceous or Nanushuk series, both occurring- in the Arctic slope 

 region. Judging from this, and from the seeniing-ty close relationship of the Berg- 

 man series to the Lower Cretaceous or Koyukuk series, and the bituminous character 

 of its coal content (No. 187 in table of analyses, p. 114), it seems probable that on 

 further investigation the Bergman series is more likely to prove to be Cretaceous 

 than Tertiary. 



NANUSHUK SERIES ( UPPER CRETACEOUS). 



Character and occurrence. — This series is named from Nanushuk River, the native 

 name of the stream on which it occurs, and which flows into the Anaktuvuk north of 

 the middle of the belt. The series lies north of the Anaktuvuk series, which it seems 

 to overlie unconformably, and is itself in turn overlain by the Tertiary Arctic coast 

 strata, with which its relations are apparently also unconformable. The unconform- 

 ity between the Anaktuvuk and the Nanushuk is inferred from the difference in the 

 topography and the marked change in the character and attitude of their rocks. In 

 the most northern observed exposure of the Anaktuvuk the dip is north, while in 

 the most southern of the Nanushuk it is steeply south. The north-south width of 

 the series, in the region of the Anaktuvuk, is about 30 miles, while its east-west 

 extent is not known. It is probable that to the east it is soon delimited by the 

 Anaktuvuk series, lying between it and the Paleozoics at the foot of the range. 

 Westward, or rather northwestward, it may possibty extend to the Arctic coast, 

 in the region between Point Barrow and Wainwright Inlet, but of this we have no 

 paleontologic evidence. 



Along Anaktuvuk River the topography of the Nanushuk series is of a character 

 intermediate between that of the gently undulatory region of the Lower Cretaceous 

 or Anaktuvuk series and that of the flat Tertiary coastal plain, whose terranes will 

 be next described. 



The rocks of the Nanushuk series are best exposed in the north bank of the 

 Anaktuvuk about 5 miles above the mouth of Tuluga River. The exposure occurs 

 in a bluff about three-eighths of a mile long that rises steeply 120 feet above the 

 river (PL XII, A). The rocks, which here have a steep dip, are mainly thin bedded 

 (PI. XII, B). The beds range from 3 to 6 inches in thickness and exhibit rapid 

 alternation. They consist of gray and brown sandstone, generally fine grained and 

 sometimes friable, with some gray and impure fossiliferous limestone, dark shale, 

 fine-grained gray quartzite, drab-colored and green chert, and black slate, stained 

 reddish along the joints. Coal of good quality is also present (see analysis 107, 

 p. 114). The beds strike N. 82° E., and dip south at an angle of 80°. 



The above exposure seems to represent part of the south or upstream limb of 

 an anticlinal fold which has been beveled off by erosion, for farther downstream the 

 dip is north. Similar beds, probably belonging to the same series, were encountered, 



