THE PRE-GRANITE COMPLEX 289 



DISTRIBUTION 



Patches of similar rocks with similar structural relationships extend 

 across the whole of the northern part of the Province of Manitoba, a 

 distance of over 300 miles east and west. Similar rocks, with apparently 

 similar relations, are also found in Ontario — the Churchill Eiver area, 

 in the northern part of Manitoba, and the Eice-Wanipigow and Star 

 Lake areas, in the southern part of the province. 



LITHOLOGY 



The main facts concerning the lithology of the series have already been 

 mentioned, namely, the dominant clastic character of the sediments and 

 the presence of interbanded volcanics. 



Most of the sediments are arkosic in character; for, although many of 

 the gneisses are thoroughly recrystallized and their feldspar content is 

 largely secondary in origin, nevertheless the proportions of the feldspars, 

 quartz, and micas show that the original rock must have contained con- 

 siderable feldspar. 



SUCCESSION 



The general succession has also been referred to. In the clastic rocks 

 recurrent horizons of conglomerate are common. There is also an ab- 

 sence of any definite succession of conglomerate, sandstone, and shale, as 

 might be expected under marine conditions with an advancing or retreat- 

 ing shoreline. 



THICKNESS 



There is great variation in thickness in different localities. Locally, 

 there is evidence that some of the sedimentary gneisses attain a thickness 

 of several thousand feet. 



BEDDING 



In places where the rocks have been less highly altered, lines of bed- 

 ding can be determined by variations in color or texture. In the con- 

 glomerate, bedding can in most exposures be determined by coarse and 

 fine bands; in some of the fine-grained gneisses, by the color banding; 

 in some of the mica schists, by crystals of secondary silicates, such as 

 garnet, staurolite, and cyanite, which stand out in rows and fairly cer- 

 tainly mark bedding planes. In much of the series, however, it is difficult 

 to ascertain absolutely the original structure. 



The conglomeratic bands in the gneisses offer some suggestive features. 

 Most of them are local and irregular ; some can be traced for a consider- 

 able distance along the strike ; others can be followed for only a few hun- 



