proceedings: geological society 253 



the western half of the chain. The Arctic Mountain system is con- 

 tinued east of the boundary by some mountains of lesser altitude. 

 These end in a scarp at the Mackenzie delta, east of which they have 

 not been recognized. 



The Arctic Slope region has two subdivisions, the Anaktuvuk 

 Plateau and the Coastal Plain. The first forms a piedmont plateau 

 sloping northward from the base of the range. Along the Colville 

 River it has a width of about 50 miles, but it narrows to the east. 

 At the boundary it appears to be entirely absent, for here only a nar- 

 row coastal plain intervenes between the mountains and the sea. The 

 westward extension of Anaktuvuk Plateau is unexplored. On the 

 north the plateau is bounded by a scarp which separates it from the 

 Coastal Plain. This plain varies from a width of less than 10 miles 

 at the bounary to over 150 south of Point Barrow. 



All of the features described, except those of the Arctic Slope region, 

 form a part of the North American cordillera. Tectonically, however, 

 the Arctic Mountain system is a discordant element in this cordillera. 

 Its structures parallel the Arctic Ocean, and its folding was probably 

 caused by movements from the Polar Sea. Tectonically and possibly 

 physiographically it is to be correlated with the Werojanski Range and 

 its northeastward extension of Siberia. 



The 306th meeting was held in the lecture room of the Cosmos Club 

 on March 8, 1916. 



REGULAR PROGRAM 



C. F. Bowen: Review of the stratigraphy and structure of the Hanna 

 Basin, Wyoming. 



In the early Territorial surveys under King, Hayden, and Powell 

 the 20,000 feet of coal-bearing rocks overlying the uppermost marine 

 sediments of the Hanna Basin — the Lewis shale — were grouped in 

 a single formation, for which the name Laramie was adopted. 



In 1907, A. C. Veatch (U. S. Geol. Survey Bull. 316, p. 246. 1907.) 

 subdivided this group into two formations which he designated as 

 "Upper and Lower Laramie." Correlating a conglomerate at the 

 base of the "Upper Laramie" on the west side of the basin with a con- 

 glomerate that marked a pronounced unconformity on the east side 

 of the basin, he announced that the "Upper and Lower Laramie" were 

 separated by an unconformity that involved the removal of 20,000 

 feet of strata. Veatch's upper division became the type of the "Upper 

 Laramie" formation, and the flora which it yielded was adopted as a 

 standard for comparison in other fields. 



Recent detailed work over three quadrangles in the Hanna Basin 

 has demonstrated that the unconformity which Veatch assigned to the 

 base of the "Upper Laramie" is really near the middle of that forma- 

 tion or 6,500 feet above the position to which he assigned it. The 

 "Upper Laramie" of Veatch is thus divisible into two formations sepa- 



