188 D. D. CAIRXES SECTION ALOXG YUKOX-ALASKA BOUNDARY 



both, sides of tlie Porcupine for a nmnber of miles both above and below 

 the mapped five-mile strip, and continue to the south of the river along 

 the boundary- line for about -i miles, to where they are overlain by Paleo- 

 zoic limestones and dolomites. To the south, these rocks again come 

 within the boundaries of the mapped area at a point about 5 miles south 

 of Ettrain Creek, and continue southward along the eastern edge of this 

 belt to within half a mile of Cathedral Creek, a distance of about 10 

 miles. From Cathedral Creek southward for 4 to T miles these rocks ex- 

 tend over the entire width of the mapped belt, and to the east of this belt 

 they were seen to be extensively developed. 



The Tindir rocks on Porcupine Eiver were noted by McConnelP* in 

 1888, and have since been described somewhat in detail by Kindle'^ and 

 ^kladdren,-^ who class them as '^^pre-Ordovician/' but have not given them 

 any formation name. To these particular rocks exposed along the Porcu- 

 pine, therefore, the writer has applied the name Tindir group. 



The membei-s of the Tindir group in this original locality consist domi- 

 nantly of quartzites, dolomites, shales, and sandstones, with which are 

 associated some intrusive greenstones. Wherever any considerable sec- 

 tion of these rocks are exposed, as along Darcy Creek, a tributar}- of the 

 Porcupine, the different members present a bright vari-colored appear- 

 ance — yellow, red, gray, and black beds being most prominent. Also 

 along Porcupine Eiver the sharp contrast between the exposures of the 

 intensely black shales and the white to grayish quartzites and dolomites, 

 which weather to a creamy or yellowish color in places, constitutes one of 

 the most striking scenic features of the Upper Eampart gorge in the 

 vicinity of the boundar}' line. 



This entire group of rocks has been considerably folded, faulted, and 

 distorted, so that it is difficult to estimate the aggregate thickness of the 

 beds in sight, and the bottom of the group was not observed. It would 

 appear, therefore, that this group of rocks on the Porcupine has a thick- 

 ness of at least 5,000 feet and may be much thicker in places. 



The shales, being softer and less competent to resist the various stresses 

 and strains to which they have been subjected, have become much more 

 crumpled, mashed, broken, and distorted than the dolomites and quartz- 

 ites, and witliin a few feet in places folds may be observed in all attitudes, 

 ranging from upright to completely reversed, with numerous faults of 



2* R. G. McConneU : Report on an exploration in the Yukon and Mackenzie basins. 

 Northwest Territory. Geol. and Nat. Hist, Surv. of Canada, Ann. Rept., vol, iv, 1888- 

 1889,. part D, pp. 129-134. 



^ E. M. Kindle : Geologic reconnaissance of the Porcupine Valley, Alaska. Bull. Geol. 

 Soc. Am., vol. 19, 1908. pp. 320-322. 



^ A. G. Maddren : Geologic investigations along the Canada- Alaska boundary. U. S, 

 Geological Survey, Bull, 520-K, 1912, pp. 6-11. 



