394 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



In the faunas of the Halleck Harbor section Dr. Girty reports both the upper and lower 

 series of the Gschelstufe or upper Carboniferous faunas to be represented. This section, which 

 is located on the north side of Saginaw Bay, Kuik Island, follows: 



Feet. 



(6) Light-gray limestone, locally cherty; foBsils abundant 450± 



(a) Black carbonaceous shales, with interbedded dark calcareous sandstones, arranged in belts, 



in which shales and sandstones alternately predominate 125+ 



At one point the shales and sandstones of division a are seen to pass along the bedding 

 directly into cherts similar to those of Pybus Bay. The fauna of this lower division of the 

 section comprises [many species which have been determined by Girty.] 



P 6-7. NORTHERN BASE OF THE ST. ELIAS RANGE AND WHITE RIVER BASIN, ALASKA 



AND YUKON TERRITORY. 



Moffit and Knopf '"'° describe the Carboniferous of the Nabesna- White River 

 region as follows : 



Upper Carboniferous deposits are represented in the headwater region of Copper River 

 by the Mankomen formation.*^ This formation is a series of sediments, between 6,000 and 7,000 

 feet thick, composed of sandstones, shales, limestones, and tuffaceous beds with included lava 

 flows and intruded sheets. These beds were originally described as Permian but should be 

 correlated, on both structural and fossil evidence, with the beds along White River and would 

 now be called upper Carboniferous. The Mankomen formation, as described by MendenhaU, 

 "falls naturally into two divisions — an upper, prevailingly calcareous division, which includes 

 somewhat more than half the total thickness, and a lower, prevailingly arenaceous and tuffa- 

 ceous division, over 2,000 feet thick." Two principal limestones are present in the upper part 

 of the Mankomen formation. The lower, a white massive limestone about 500 feet thick, is 

 separated from the upper, which is about 600 feet thick, by several hundred feet of shale. This 

 upper limestone is made up of thin beds and is highly fossiliferous, much more so than any 

 other parts of the section examined. Fossils were collected at several horizons from the base 

 to the top of the Mankomen section, and the correlation with the Wliite River section is made 

 on their evidence. The Mankomen resembles the Nabesna-White Carboniferous section in 

 the presence of much volcanic material, in which respect both differ from the corresponding 

 Yukon Carboniferous. 



A massive limestone, having a maximum thickness of more than 2,000 feet, is found in 

 the Chitina Valley and reaches its greatest development on Chitistone River, which heads 

 near Skolai Pass. This formation is known as the Chitistone limestone and was correlated 

 by Schrader and Spencer in their report in 1901 on the geology of the Chitina Valley* with 

 the Carboniferous limestone of White River. They found no determinable fossils in the Chiti- 

 stone limestone, and the correlation was based on stratigraphic evidence and lithologic simi- 

 larity. After studying the Carboniferous formations of the Upppr Copper River valley, Men- 

 denhaU" questioned this correlation, his objections being based on the seeming absence of 

 fossils in the Chitistone limestone, on its conformable relation to the overlying Triassic sediments, 

 and on its freedom from basic intrusives, all of these features being contrary to the character 

 of the Carboniferous sediments of the Mankomen formation. Later work,'' however, proved 

 the Chitistone limestone to be of Triassic age, but it is suggested that the Nikolai greenstone, 

 which conformably underlies the Chitistone limestone in the Chitina Valley, may probably 



^ MendenhaU, W. C, The geology of the central Copper River region, Alaska: Prof. Paper U. S. Geol. Survey 

 No. 41, 1906, pp. 40-52. 



b Schrader, F. C, and Spencer, A. C, The geology and mineral resources of a portion of the Copper River district, 

 Alaska, a special publication of the TJ. S. G'eol. Survey, 1901, p. 46. See also Bull. U. S. Geol. Survey No. 374, 1909, 

 p. 27. 



MendenhaU, W. G., op. cit., p. 51. 



<^ Moffit, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitina region, Alaska: Bull. U. S. Geol. 

 Survey No. 374, 1909, p. 26. 



