184 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



The earliest history of this whole region (Nabesna, White, Copper, and 



Chisna Rivers) — 



"shows that marine conditions prevailed throughout the region, but that the 

 normal course of sedimentation was repeatedly interrupted by the extrusion of 

 andesitic and basaltic lavas and the ejection of tuffs and breccias. Where the 

 accumulation of ordinary clastic sediments went on uninterruptedly, sandstones, 

 shales, and limestones were laid down, and now bear evidence in their wealth of 

 fossil remains, that the seas teemed with life, among which huge zaphrentoid 

 corals flourished in great abundance. The marine occupation appears to have 

 continued until early Mesozoic time." ' 



In central Alaska, Prindle- reports Permian or Pennsylvanian rocks in 

 the Fairbanks and Rampart Quadrangles of the Yukon-Tanana region. 

 These consist of gray, greenish and black shale with siliceous beds. Prindle,^ 

 writing upon the Fairbanks Quadrangle, gives the following list: Gray and 

 black shale, with some chert, and probably some limestone resting uncon- 

 formably on the beds below. This series is regarded as equal to the Nation 

 River series of the Yukon, but may be equal in time to the unconformity 

 between the Nation River and the Calico Blufif (Mississippian). 



Brooks and Kindle* report for the Upper Yukon a heavy limestone 

 (Gschelian in age) unconformably above a mass of sandstone and shale, 

 3,700± feet thick, with fragments of plants and some small seams of bitumi- 

 nous coal. There are two layers of conglomerate, one at the base, very mas- 

 sive, and a second, not so heavy, about 1,000 feet above the base. 



Invertebrates are reported from a heavy limestone 'just below an un- 

 conformity in the Upper Yukon region, which Girty considers as Gschelian 

 in age, the same fauna as at Pybus Bay, Kuiu Island. The rocks are not 

 metamorphosed in this region and there is no evidence of volcanic activity, 

 except at Glenn Creek. 



In the upper part of the Tanana Basin, Schrader^ reports Permian fossils 

 in the Suslota limestone, which lies above the Nabesna limestone. 



Keele" and Camseir found a limestone between the Peele and Stewart 

 Rivers which is probably the equivalent of the massive limestone of the 

 Yukon area. This limestone is a "massive, granular limestone containing 



1 Moffit, F. H., and Adolph Knopf, Mineral Resources of the Nabesna-White River District, 



Alaska, U. S. Geological Survey Bull. 417, p. 47. IQIO- 



2 Prindle, L. M., The Fairbanks and Rampart Quadrangles, Yukon-Tanana Region, Alaska, 



U. S. Geological Survey Bull. 337, 1908. 



3 Prindle, L. M., A Geologic Reconnaissance of the Fairbanks Quadrangle, Alaska, etc., 



U. S. Geological Survey Bull. 525, 1913. 

 " Brooks, A. H., and E. M. Kindle, Paleozoic and Associated Rocks of the Upper Yukon, 



Alaska, Bull. Geol. Soc. Amer., vol. 19, p. 255, 1908. 

 5 Schrader, F. C, Recent Work of the United States Geological Survey in Alaska, Bull. 



Amer. Geog. See, vol. 34, pp. 1-145. 1902. 

 ^ Keele, Jos., Report on the Upper Stewart River Region, Yukon, Annual Report Canadian 



Geological Survey, vol. 16, pt. c, p. 14, 1906. 

 ' Camsell, Chas., Report on the Peele River and Tributaries, Yukon and Mackenzie, Annual 



Report Canadian Geological Survey, vol. 16, pt. cc, p. 16, 1906. 



