PRE-CAMBRIAN OF NORTHERN ONTARIO AND QUEBEC 311 



the conglomerate. All these rocks are greatly broken up by in- 

 trusive dikes and masses of porphyry. 



Lying on the upturned edges of these rocks is a' second con- 

 glomerate, a massive rock composed almost entirely of greenstone 

 fragments with about 10 per cent of granite pebbles, lying flat, and 

 showing vague cross-bedding in places. This conglomerate occurs 

 in irregular patches and knobs, evidently erosion remnants, lying 

 indifferently on the older slates, greywackes, grits, and conglom- 

 erates. The writer concluded from the composition, which is 

 characteristic of the base of the Cobalt conglomerate, and from 

 the lack of deformation that it is an erosion remnant of the Cobalt 

 conglomerate found to the east in larger masses ; the areal relations 

 to the underlying sedimentary series show that there is a large 

 unconformity between the two. 



The earHer geologic maps show a number of patches of con- 

 glomerate, mapped as Cobalt series, lying to the north of the 

 areas of Larder slate, in many cases some distance to the north 

 and within areas of Keewatin. These conglomerates proved on 

 examination to consist invariably of beds dipping to the south at 

 angles varying from 60 to 90, and frequently badly sheared. Their 

 composition is like that of the conglomerate of the Larder townsite, 

 in that the pebbles are largely of rhyolite, banded chert, jasper, 

 and iron formation, with some basalt, although commonly the 

 proportion of rhyolite is larger and that of iron formation smaller 

 than on the townsite. The rocks to the north of the conglomerate 

 band are invariably basalts except around Malone Lake, where 

 rhyolite occurs; and almost invariably they exhibit pillow struc- 

 tures and other characteristics of lavas. The conglomerates were 

 found to form, not isolated patches, but a strong band, continuous 

 throughout the district, except where broken by intrusive masses 

 of porphyry, and where, for a short distance to the east of Barber 

 Lake, it has been obliterated by thinning and intense shearing. 



The rocks to the south of the conglomerate band were then 

 carefully examined, as some of them had been previously mapped 

 as Keewatin. A great deal of excuse for the earlier mapping was 

 found, in that in many cases the rocks are massive, dark green, 

 chloritic rocks, indistinguishable in the average hand specimen 



