270 BROOKS AND KINDLE PALEOZOIC ROCKS OF UPPER YUKON 



cal of the northern end of the section, and the mica schist of the southern 

 end. Some greenstones are present, but are relatiyely scarce. Mr Prin- 

 dle has found some crystalline limestones associated with the schists in 

 this general region, but these were not studied by the writers. The 

 granitic rocks occurring in stocks and dikes, which are not uncommon, 

 are usually massive, but are sometimes sheared along their peripheries. 



The general strike is northeasterly, with prevailingly northerly dips, 

 and usually at a steep angle. Evidence of close folding is usually found 

 where the bedrock is well exposed. The thickness of this arenaceous 

 series, to be measured in thousands of feet, can probably never be deter- 

 mined, even with the most minute stratigraphic work. 



The data at hand justify the statement that, below the rocks of laiown 

 age (certainly older than the Devonian and probably than the Ordo- 

 vician), there is a complex of metamorphic sediments and igneous rocks 

 which is widely distributed in the upper Yukon basin. As some of these 

 are probably of synchronous age with the quartzite and slates of the Por- 

 cupine river, which are below the Ordovician, we are probably justified 

 in classing them all as pre-Ordovician, with the reservation that there 

 may be some younger metamorphosed Paleozoic terrains infolded with 

 them. The evidence now at hand indicates that the rocks formerly 

 classed as "Archean basal granites" or "Basal Gneiss" are for the most 

 part altered igneoiis rocks which have been injected since the deposition 

 of the sediments. 



If one were to venture on more definite correlations, it would be to 

 regard the Birch Creek and Fortymile series, as defined by Spurr, to l)e the 

 equivalent of the Nasina series as used by McConnell and Brooks. The 

 term "Birch Creek schists," as used by Prindle in his more recent publi- 

 cations, would represent either the lower or less calcareous phase of the 

 Nasina series or might indicate a decrease in the percentage of calcareous 

 matter to the westward. The latter theory appears to be borne out by 

 the fact that the metamorphic rocks, described by Schrader north of the 

 Yukon under the names Eapid schists,*^ Lake quartzite schist, and 

 Totsen*^ series, which are here correlated with Prindle's Birch Creek 

 schist, are essentially non-calcareous rocks. A general correlation of these 

 metamorphic rocks with the Kigluaik group of the Seward peninsula*^ is 

 probably justified. The Kigluaik embraces a great thickness of gneisses, 



*i F. C. Schrader : Preliminary report on a reconnaissance In tlie Chandlar and Koyu- 

 kuk rivers, Alaska. Twenty-first Annual Report, U. S. Geological Survey, part ii, pp. 

 473-474. 



*2 F. C. Schrader : Reconnaissance in northern Alaska. Professional paper no. 20, IT. S. 

 Geological Survey, pp. 58-60. 



" Arthur J. Collier, Frank L. Hess, and Alfred H. Brooks : The gold placers of a part 

 of the Seward peninsula. Bulletin no. 338, U. S, Geological Survey. (In print,) 



