300 BROOKS AND KINDLE PALEOZOIC ROCKS OF UPPER YUKON 



The Eampart region has yielded some Upper Carboniferous fossils, 

 found in a gray and black argillaceous and siliceous slate by Prindle.^"^ 

 These rocks have been but little studied and their relation to the Devonian 

 is not known. Lithologically they do not appear to resemble either the 

 Xation river or the younger Carboniferoiis of the upper river. Spurr^''^ 

 described some limestones and carbonaceous argillites which occur on the 

 Yukon 20 miles below the mouth of Minook creek, and on the basis of 

 some fragmentary fossil plants assigned them to the Tahkandit. 



A heavy conglomerate and argillite series in the White Eiver region,^"* 

 termed the Willesley formation, was provisionally assigned to the Carbon- 

 iferous or Devonian on the basis of a few invertebrate fossils. It seems 

 quite possible that this may be a synchronous deposit with the Nation 

 Elver. 



In the Upper Copper Eiver basin MendenhalP^^ found a series of con- 

 glomerates, quartzites, and tuffs which he termed the Chisna formation 

 and provisionally correlated with the Willesley. A heavy conglomerate 

 also occurs along the western foot of the Alaska range, and this, too, may 

 be Carboniferous. 



If these conglomerates are synchronous deposits, they probably repre- 

 sent a far-reaching period of erosion. In the Copper-White Eiver region 

 it appears to be the oldest recognizable Paleozoic, resting immediatel}^ on 

 the metamorphic rocks. If it proves to be Nation Eiver, it indicates that 

 the Calico Bluff, the Devonian, and possibly Silurian rocks were removed 

 by erosion before its deposition in this region. 



Upper Carboniferous terrains find an extensive development in the 

 Copper- White Eiver area where the Mankomen formation has been de- 

 scribed by Mendenhall."^ This includes 6,000 to 7,000 feet of sand- 

 stones, shales, and limestones, with much igneous material. These rocks, 

 referred to the Permian, would here be classed as Upper Carboniferous 

 and can be correlated provisionally with the highest Carboniferous horizon 

 of the Yukon. The Yukon rocks include, however, only deep-sea sedi- 

 ments, while the rocks described carry a large amount of clastic as well as 

 igneous material. If, then, these terrains are S5rnchronous deposits, the 



i"' L. M. Prindle : The Fairbanks and Rampart quadrangles. Bulletin no. 337, V. S. 

 Geological Survey. (In print.) 



i»* J. E. Spurr : Eighteenth Annual Report, U. S. Geological Survey, part iii, pp. 171- 

 172. 



1™ Alfred H. Brooks : A reconnaissance in the White and Tanana River basins. Twen- 

 tieth Annual Report, V. S. Geological Survey, part vii, pp. 471-472. 



110 Walter C. Mendenhall : Geology of the central Copper River region, Alaska. Pro- 

 fessional paper no. 41, U. S. Geological Survey, pp. 33-36. 



^^ Walter C. Mendenhall : The geology of the central Copper River region, Alaska. 

 Professional paper no. 41, U, S. Geological Survey, pp. 40-52. 



