284 ALCOCK AND BRUCE PRECAMBRIAN ROCKS OF MANITOBA 



as fragments of other types. The volcanic and sedimentary rocks occur 

 as a narrow band between great areas of red granite which is intrusive 

 into them. South of Star Lake an isolated boss of a granitic rock in- 

 trudes both the conglomerate and the volcanics. It shows a considerable 

 degree of variation. In places it is a hornblende syenite, in others a 

 binary granite. 



CHURCHILL RIVER AREAS ^^ 



Though the Churchill Eiver flows throughout most of its course over 

 granite and granite-gneiss, a few local areas of schists and sediments are 

 found. One of the largest of these bands is situated about 10 miles east 

 of the outlet of Southern Indian Lake. The dominant rock type is a dark 

 gray, sheared quartzite containing considerable quantities of sericite. It 

 stands at a high angle and is cut by gray granite and dikes of pegmatite. 

 A few small patches of hornblende and chlorite schists occur along the 

 river; they are associated with finely banded gneisses traversed by peg- 

 matite dikes. 



The granites and gneisses which intrude these rocks consist of both 

 gray and red varieties and include both biotite and hornblende-bearing 

 types. One variety of red granite is porphyritic and appears to be 

 younger than the regional gneiss. 



In the vicinity of Fort Churchill is a sedimentary formation consisting 

 of arkose and quartzite. The beds stand at a high angle and are cut 

 everywhere by small quartz veins. Hence, though no contact with the 

 granite was observed, it is concluded that it is older than the granite. It 

 is, however, different lithologically from the pre-granite schists, is much 

 less highly metamorphosed, and has accordingly not been classed with 

 them. It is possible that it occupies a position similar to that of the 

 Missi series of the Lake Athapapuskow district. 



NARROW LAKE AREA ^'^ 



The Narrow Lake area lies on a canoe route between Nelson House 

 and Southern Indian Lake, in approximate latitude 59° and longitude 

 99° west. It is a small area, with a length of but eight miles, situated 

 immediately west of Narrow Lake, an expansion of the Eat Eiver. 



Tlie rocks of the area consist of a narrow belt of sediments and vol- 

 canics intruded on either side by massive, red granite. The pre-granite 

 series pinches out to the northeast; to the southwest it also narrows, and 



12 F. J. Alcock : Geol. Surv. Can., Sum. Kept., 1915, p. 133. 



13 F. J. Alcock : The Rat River route from Tbreepoint Lake to Southern Indian Lai:;-. 

 Geol. Surv. Can., Sum. Rept., 1920. 



