SILURIAN 273 



"The chief interest of the collection lies in tlie lamelli-branch fragments, 

 which represent a very large thick-shelled form, which it appears almost cer- 

 tain is specifically identical with a shell occurring in the Glacier Bay lime- 

 stones and similar beds at Freshwater bay, in southeastern Alaska. This shell 

 has been referred to the genus Megalomus in southeastern Alaska and consid- 

 ered to belong to a late Silurian fauna. 



"The apparent identity of the Quail Creek specimens with those at Glacier 

 bay makes it highly probable that the two limestones are of the same age, thus 

 indicating a late Silurian age for the limestones of Quail creek." 



Though this determination indicates a Silurian age for the limestone, 

 it is b)^ no means certain that the associated fragmental rocks belong to 

 the same terrain. Therefore, while it is safe to assume that the Silurian 

 is present in this district, some of the rocks which have been assigned to 

 it nuiy be of Devonian age. On the other hand, it will be shown that 

 some of the rocks, including slates, limestones, and qiiartzites, exposed 

 along the upper Yukon and here assigned to the Devonian, may be of 

 Silurian age. 



It seems probable that this aggregate of rocks comprises a thickness of 

 several thousand feet, but,- as it is extremely intricately folded, estimates 

 of thickness are little more than guesses. These terrains strike north- 

 easterly toward Beaver creek, where a belt of similar rocks has been found 

 by Prindle^^ and Hess flanked by Devonian beds. 



A late Silurian faima, to Avhich the Quail Creek fauna is closely re- 

 lated, is also known to occur at Glacier^- and at Freshwater"^ bays, in 

 southeastern Alaska. These are clearly younger than the fauna of the 

 Porcupine district already referred to. The unique character of this 

 fauna does not suggest comparison with any other known SiliTrian fauna 

 save in a most general way. It is supposed to represent a horizon near 

 that of the Guelph. 



The facts presented show an extensive development of Silurian deep 

 sea sediments in the Porcupine district, the possible presence of similar 

 rocks in the Yukon section, and the probability tliat a group of frag- 

 mental rocks extensively developed in the Eampart region belongs to the 

 same system. Eegarding the Silurian of other parts of the territory it 

 has only been definitely recognized as a heavy limestone bed in south- 

 eastern Alaska, which will be described below. The Port Clarence'' 



=1 L. M. Prindle and F. L. Hess: The Rampart gold placer region, Alaska. Bulletin 

 no. 280, U. S. Geological Survey, pp. 18-20. 



°- A. H. Brooks : A preliminar.v report on the ICetchikan mining district, Alaska. Pro- 

 fessional paper no. 1, U. S. Geological Survey, 1902, p. 19. 



=■■3 E. M. Kindle : Notes on the Paleozoic faunas and stratigraphy of southeastern 

 Alaska. Journal of Geology, vol. xv, 1907, p. 323. 



"■* Arthur .T. Collier, Frank L. Hess, P. S. Smith, and Alfred H. Brooks : The gold 

 placers of parts of the Seward peninsula. Bulletin no. 328, U. S. Geological Survey, 

 pp. 73-79, 



