SEDIMENTARY EOCKS 



199 



not been very definitely defined paleontologicall}'-, but from the fossils 

 that have been reported it would appear that the Lower Cache Creek 

 group includes the Eacquet group. 



Nation Elver formation. — A series of beds which have been tentatively 

 correlated with the Nation Eiver formation extend along the boundary 

 line more or less persistently for a distance of about 9 miles in the vicinity 

 of Yukon Eiver between Tatonduk Eiver and Eagle Creek. This forma- 

 tion consists dominantly of conglomerates, sandstones, and shales, and has 

 a thickness of at least 4,000 feet. The pebbles in the conglomerate beds 

 are composed dominantly of chert, and range in most places from about 

 1/32 of an inch to 1 inch in diameter. The sandstones are characteris- 

 tically grayish to brownish, medium textured, hard, firm rocks, which 

 weather in most places to a brownish color; occasional yellowish or red- 

 dish appearing beds, however, occur. The shales are prevailingly grayish 

 to yellowish in color and dominantly argillaceous in composition. 



The lowest member of this formation on McCann hill is a massive con- 

 glomerate bed about 60 feet in thickness. Overlying this basal conglom- 

 erate are about 230 feet of brownish to nearly black sandstones of the 

 same composition dominantly as the conglomerate, but in a finer state of 

 eomminution. These sandstones are followed by a second conglomerate 

 bed 25 to 30 feet thick, which is in turn overlain by sandstones, shales, 

 and occasional intercalated conglomerate beds. These two lower con- 

 glomerate beds appear to be quite persistent and characterize the bottom 

 of the formation along the boundary. 



These beds appear undoubtedly to belong to the Nation Eiver forma- 

 tion** of Alaska, which is considered to be of Carboniferous and probably 

 of Pennsylvanian age. This formation along Nation Eiver near the Yu- 

 kon, where it is most typically exposed, corresponds very closely litho- 

 logically with these beds along the boundary, and occupies a correspond- 

 ing stratigraphical position. In both localities, also, the beds character- 

 istically contain abundant plant remains. 



Permo-Carboniferous ( ?) conglomerate — Possibly consolidated boulder 

 clay.— On the extreme western edge of the belt under consideration along 

 the Yukon-Alaska boundary line, and just north of Tatonduk Eiver, a 

 peculiar conglomerate is developed. This extends over an area only about 

 one mile in diameter within the mapped area, but was seen to have a more 

 extensive development to the west. 



This conglomerate is at least 700 or 800 feet in thickness, and consists 

 dominantly of a firm, somewhat dense, finely textured, reddish, argilla- 



« A. H. Brooks and E. M. Kindle : Paleozoic and associated rocks of the Upper Yukon, 

 Alaska. Bull. Geol. Soc. Am., vol. 19, 1908, pp. 294, 295, 



