234 J- M. BELL 



ous quartz veins which it contains, though it has within the last few 

 years •become more important as an iron-ore producer. One mine — 

 the Helen — exports more ore annually than all the other iron mines 

 in Canada put together. Lying within the boundaries of the division 

 is the Michipicoten Huronian area, and to the southwest of the 

 division, and in part within it, is the Pucaswa Huronian area, sepa- 

 rated from the Michipicoten area by granite of later age than either. 



The Michipicoten Huronian rocks constitute a band from four to 

 twelve miles in width, which extends northward from a point a few 

 miles south of Point Gargantua, on the Lake Superior Shore, to a point 

 about 14 miles south of the main line of the Canadian Pacific Railway, 

 "'^rom this point an arm extends both east and west. The" w^estern 

 arm, which is the longest and most important, stretches westward 

 from the Magpie River, which may be taken as the center of the 

 north-and-south arm, for a distance of about 40 miles, where it is 

 cut off by granitic rocks. The eastern arm extends eastward from 

 the Magpie River for about 25 miles, and is intercepted by granitic 

 rocks in the neighborhood of Dog Lake. South and southwest of 

 the western arm lie small patches of Huronian rocks which compose 

 the Pucaswa area. The Pucaswa^ area would naturally be included 

 within the Michipicoten area, because of the similarity in the lithology 

 of each and on account of their proximity, were it not that the Pucaswa 

 Iron Range is quite separate and distinct from the Michipicoten Iron 

 Range in geographical position, and differs markedly in structural 

 features. 



The boundaries of the Huronian rock in both the Michipicoten 

 and Pucaswa areas are extremely irregular, but everywhere the 

 bordering rocks are composed of granite or rocks of allied petro- 

 graphic species. The outer boundary is formed by granitic rocks 

 which are apparently part of the great Laurentian acid eruptive 

 complex of central Canada, which extends northward to within 60 

 miles of Hudson Bay, and southeastward to the original Huronian 

 area of Logan and Murray — a distance of 120 miles. The inner 

 boundary of the Michipicoten area is an immense granitic batholith 

 with principal dimensions of 19 miles from north to south by 28 miles 



I In the paper by the writer in the Bureau of Mines Report for 1905 the Pucaswa 

 area is called the North Michipicoten area. 



