80 RECONNAISSANCE IN NOBTHEBN ALASKA IN L901. 



but not examined, about l 11 or 12 miles above ihi- point on the opposite side of the 

 valley. Northward toward the Colville, where t ln-\ arc finally succeeded by the 

 younger formation of the Tertiary coastal plain, the beds seem to lie more nearly 

 horizontal. They possibly lloor the valley and form the bed of Colville River 

 down to about "> miles below the mouth of the Anaktuvuk. Here are rapids which 

 probably mark the termination of the series in the river bed, though the rocks are 

 no longer exposed in the banks. Below this point the bed of the Colville appears to 

 lie in the younger and softer formations of the coastal plain, and the current continues 

 >lack nearly all the way to the coast. 



Structure. — So far as observed, the strike of the Nanushuk series is about east and 

 west, and though, from comparison with some of the older rock series, we might 

 expect the prevailing dip to be northward, observation has hardly been sufficient to 

 affirm that it is so. The apparent existence of at least one pronounced anticline lias 

 been shown in the previous paragraph. The series is traversed by a system of 

 approximately horizontal jointing (PI. XII, B). 



Age. — On paleontologic evidence the Nanushuk series is assigned to the Upper 

 Cretaceous. The fossils were nearly all collected in the locality above described — on 

 the north bank of the Anaktuvuk 5 miles above the mouth of the Tuluga. They 

 have been identified by Dr. T. W. Stanton, who reports the lot to be certainly of 

 Upper Cretaceous age. The forms identified are as follows: 



Fossils of the Nanushuk series from bank of Anaktuvuk River 5 miles above mouth of Tuluga River. 



Inoeeramus, a rather large species, fragmentary specimens. 



A small Astarte, numerous specimens. 



Nucula, numerous specimens. 



Avicula. 



Peotunculus, several specimens. 



Thracia. 



Tellina, 2 species. 



Siliqua. 



Modiola. 



Scaphites. 



Haminea. 



Besides the above, there are casts and impressions of numerous bivalves not yet 

 determined. 



Concerning the above list, Doctor Stanton remarks that the species are all appar- 

 ently different from those with which he is familiar, but that several of them are of 

 types known only in the Upper Cretaceous. 



Correlation. — Upper Cretaceous rocks occur also to the south of the Endicott 

 Mountains in the Koyukuk and Yukon Basin, between the southern edge of the 



