INTO HURONIAN AND LAURENTIAN. 441 



tuting the group which is rendered of such economic importance, from 

 its association with copper lodes. The group consists of the same 

 silicious slates and slate conglomerates, holding pebbles of syenite in- 

 stead of gneiss ; similar sandstones sometimes shewing ripple-mark, 

 some of the sandstones pale sea-green ; and similar quartzose conglo- 

 merates, in which blood-red jasper pebbles become largely mingled 

 with those of white quartz, and in great mountain masses predominate 

 over them. But the series is here much intersected and interstratified 

 with greenstone trap, which was not observed on Lake Temiscamang. 



These rocks were traced along the north shore of Lake Huron, 

 from the vicinity of Sault Ste. Marie, for 120 miles, and Mr. Murray 

 ascertained that their limit on the Lake Shore occurred near 

 Shebahahnahning, where they were succeeded by the underlying 

 gneiss. 



The position in which the group was met with, on Lake Temis- 

 camang, is 130 miles to the north-east of Shebahahnahning, and last 

 year Mr. Murray, in exploring the "White-Fish river, was enabled to 

 trace the out crop of the group, characterized by its slates, sandstones, 

 conglomerates, greenstones, and copper lodes, for sixty-five miles from 

 Shebahahnahning to the junction of the Maskinonge and Sturgeon 

 rivers tributary to Lake Nipissing. The general bearing of the out- 

 crop is N.E., and an equal additional distance, in the same direction, 

 would strike the exposure on Lake Temiscamang. In the portion 

 which Mr. Murray examined last year, the dip appears to be about N.W., 

 often at a high angle, while that of the subjacent gneiss is more gen- 

 erally S.E. ; sometimes at a low angle, and in some places nearly 

 horizontal. 



To the eastward of this out-crop, Canada has an area of 200,000 

 square miles. This has yet been but imperfectly examined, but in so 

 far as investigation has proceeded, no similar series of rocks has been 

 met with in it ; and it may safely be asserted that none exists be- 

 tween the basset edge of the Lower Silurian and the group from 

 Shebahahnahning to the Mingan Islands, a distance of more than 1,000 

 miles, and probably still farther to Labrador. 



The group on Lake Huron, we have computed to be about 10,000 

 feet thick ; and from its volume, its distinct lithologicai character, its 

 clearly marked date posterior to the gneiss, and its economic im- 

 portance as a copper-bearing formation, it appears to me to require a 

 distinct appellation, and a separate color on the map. Indeed, the in- 

 vestigation of Canadian Geology could not be conveniently carried on 

 without it. "We have, in consequence, given to the series the title 

 of Huronian. 



VL. II. — E* 



