298 BROOKS AND KINDLE rALEOZOIC ROCKS OF UPPER YUKON 



stones, carbonaceous argillites, and conglomerates which he called the 

 "Tahkandit series," and assigned to the Upper Carboniferous on the basis 

 of Schuchert's determination of the fossils in the limestones. This group 

 appears to comprise the three subdivisions of the Carboniferous which 

 have been described above. The Tahkandit, as defiued hj Spurr, can 

 therefore be regarded as the equivalent of the entire Carboniferous sec- 

 tion of the Yukon. 



Carboniferous rocks are known to occur in many widely separated local- 

 ities in Alaska besides the upper Yukon valley. In but few of these have 

 the studies gone into sufficient detail to permit of a subdivision into for- 

 mations. In tlie Porcupine basin, in southeastern Alaska, in the head- 

 water region of the Copper, Tanana, and White rivers, and at cape Lis- 

 burne, however, some of the details of the stratigraphic succession have 

 been determined and certain correlations with the Yukon section can at 

 least be suggested. 



Along the Porcupine river the Lower Carboniferous section resembles 

 the Calico Bluff formation, as seen along the Yukon, in being composed 

 largely of interbedded shales and limestones, but differs from it in having 

 a larger percentage of drab-colored shales, which are often arenaceoiis and 

 tough instead of fissile and black (see page 331). The presence of this 

 same Lower Carboniferous horizon in the region lying northwest of the 

 Porcupine is indicated by a few fragmental fossils collected by S. J. 

 Marsh"' in the Endicott mountains near the Arctic divide, probably 20 or 

 30 miles west of the International boundary. 



In 1899 Schrader collected some fossils from the gravels of the Chand- 

 lar Eiver basin lying west of the Porcupine, which were provisionally 

 referred to the Devonian,®^ but it has since been suggested by Doctor 

 Girty"' that they are of Lower Carboniferous age. 



In the same northern Alaska region there is a crystalline limestone and 

 clay shale horizon, called by Schrader^"" the "Lisburne," which has now 

 found definite place in the Lower Carboniferous^''^ though first placed in 

 the Devonian. In the Anaktuvuk valley there is a conglomerate and 

 qi;artzite series, called by Schrader^"^ the "Stuver formation," lying be- 

 neath the Lisburne unconformably, which may be either Carboniferous 



*' The writers are indebted to Mr Marsh not only for these fossils, but also for notes 

 on the geology and maps of the region explored by him. 



"* F. C. Schrader : A reconnaissance in the Chandlar and Koyukuk basins. Twenty- 

 first Annual Report, U. S. Geological Survey, part ii, p. 476. 



s" Bulletin no. 278, U. S. Geological Survey, p. 26. 



1™ P. C. Schrader : A reconnaissance in northern Alaska. Professional paper no. 20, 

 pp. 67-72. 



i« Alfred H. Brooks: Professional paper no. 45, pp. 223-225. 



i»- Opus cited, pp. 60-62. 



