186 D. D. CAIRNES SECTION ALONG YUKON-ALASKA BOUNDARY 



no place also in the complete Paleozoic section found to occur in the dis- 

 trict for the extensive, thick, Yukon group, and it is difficult to conceive 

 how the Yukon group could be a metamorphosed phase of the Tindir 

 group, considering the compositions of the component members of the two 

 groups, and considering further that the two groups are extensively de- 

 veloped and both preserve wherever found their peculiar, distinctive, and 

 very different lithological characteristics. Furthei, just north of Yukon 

 River along the 141st meridian some phyllites occur overlying the mem- 

 bers of the Yukon group, and as these phyllites closely resemble certain 

 members of the Tindir group, and are unlike any of the other rocks seen 

 along the boundary, it seems probable that these are Tindir beds, and, if 

 so, the members of the Yukon group are decidedly the older. 



Therefore, although the typical and definitely identifiable members of 

 the Tindir group were not found by the writer in actual contact with the 

 rocks of the Yukon group, unless the phyllites previously referred to be- 

 long to the Tindir, still for the reasons above mentioned it seems as if 

 there could remain but little doubt that the members of the Yukon group 

 are the oldest rocks in the Yukon Valley and that they are of pre-Cam- 

 brian age. 



The schistose rocks of the Yukon Valley have been subdivided by vari- 

 ous writers and have been given a number of formational names, and it 

 seems probable that the greater number of these divisions are included by 

 the term Yukon group. This group thus probably includes the Nasina 

 series, as described by Brooks^^ and McConnell,^^ and also McConnell's 

 Klondike series^* and Pelly gneisses,^^ as well, possibly, as his Moosehide 

 di abase. ^^ McConnell has also correlated the Birch Creek^^ series and 

 Forty-mile series,^^ as described by Spurr, with the Nasina series, so these 

 rocks are also probably included. 



The Tanana schists as described by Brooks^^ and MendenhalP" may 



" A. H, Brooks : A reconnaissance in the White and Tanana River basins, Alaska, in 

 1898. U. S. Geological Survey, 20th Ann. Rept., part vii, pp. 465-467. 



13 R. G. McConnell : Report on the Klondike gold fields. Geol. Surv. of Canada, Ann. 

 Rept., vol. xiv, part B, 1901, pp. 12B-15B. 



" Ibid., 15B-22B. 



15 A. H. Brooks : Op. cit, pp. 460-463. 

 R. G. McConnell : Note on the so-called basal granite of Yukon Valley. The Amer- 

 ican Geologist, vol. xxx, July, 1902, pp. 55-62. 



" R. G. McConnell : Report on the Klondike gold fields. Geol. Surv. of Canada, Ann. 

 Rept., vol. xiv, part B, 1901, pp. 22B-23B. 



'" J. E. Spurr : Geology of the Yukon Gold district, Alaska. U. S. Geological Survey, 

 18th Ann. Rept., part iii, 1896-1897, pp. 140-145. 



18 Ibid., pp. 145-155. 



19 A. H. Brooks : A reconnaissance in the White and Tanana River basins, Alaska, in 

 1898. U. S. Geological Survey, 20th Ann. Rept, part vii, 1898-1899, pp. 468-470. 



2« W. C. Mendenhall : A reconnaissance from Resurrection Bay to the Tanana River, 

 Alaska, In 1898. U. S. Geological Survey, 20th Ann. Rept., 1898-1899, pp. 313-315. 



