196 D. D. CAIRNES SECTION ALONG YUKON-ALASKA BOUNDARY 



the red exposures constituting distinctive landmarks easily recognizable 

 for 10 or 20 miles or even greater distances. 



Shales and cherts similar to certain members of this series are exposed 

 on Calico Bluff, facing Yukon Eiver, and there underlie Carboniferous 

 beds of the Calico Bluff formation. These shales and cherts on Calico 

 Bluff have been provisionally assigned to the Upper Devonian on paleonto- 

 logical, stratigraphical, and lithological grounds,^^ and in all probability 

 they belong to that age, but as yet perfectly conclusive proof of this is 

 lacking. The Calico Bluff shales and cherts were, however, traced east- 

 ward to the boundary line and definitely correlated with members of the 

 shale-chert series there, which is overlain by Carboniferous shales, sand- 

 stones, and conglomerates. 



Carhoniferous — General. — The rock formations of known Carbonifer- 

 ous age, developed along the 141st meridian between Porcupine and Yu- 

 kon rivers, are here considered under three divisions or as belonging to 

 three formations. In addition, a peculiar conglomerate occurs in one 

 locality, which resembles a consolidated boulder clay, and which is prob- 

 ably also of Carboniferous or Permo-Carboniferous age. The three main 

 Carboniferous formations are the Eacquet group, the Nation Eiver for- 

 mation, and a shale series. The Eacquet group, which is developed only 

 in the northern portion of the belt along the Alaska- Yukon boundary here 

 being considered, is composed dominantly of limestone, with some shales, 

 chert and chert conglomerates, and contains both Pennsylvanian and 

 Mississippian fossils. In the southern end of the district a series of 

 conglomerates, sandstones, and shales occurs, which has been correlated 

 with the Nation Eiver formation, and is apparently the stratigraphical 

 equivalent of the lower portion of the Orange group to the north. These 

 beds overlie a series of shales and thinly bedded limestones which con- 

 tain Carboniferous fossils and possibly include the Calico Bluff forma- 

 tion. The members of the Eacquet group in the north appear to be the 

 stratigraphical equivalents of the shale series in the south, and at one 

 point in the vicinity of Et train Creek there was noted to occur what 

 appears to be a transition from the dominantly calcareous members of 

 tlie Eacquet group to the more arenaceous and argillaceous sediments of 

 the southern portion of the district. 



Shale series. — This formation appears to be about 800 or 900 feet in 

 thickness, and consists dominantly of shales, cherts, and thinly bedded 

 limestones, but includes as well occasional more arenaceous beds that re- 

 semble finely textured, calcareous sandstones. The shales range in color 

 from gray to black and are dominantly soft and friable. The cherts con- 



38 A, H. Brooks and E. M. Kindle : Bull. Geol. Soc. Am., vol. 19, Oct., 1908, pp. 286-291, 



