14 



The line of contact between the highly inclined crys- 

 talline rocks of the Pre-Cambrian and the horizontal 

 limestones and sandstones of the Palaeozoic is marked 

 by a very distinct and abrupt change in the character of 

 the country. The Pre-Cambrian region is decidedly rocky 

 and uneven and is thus in large part unsuited for purposes 

 of agriculture. It is pre-eminently a grazing country 

 with great streches of uncleared forest land still remaining. 

 In marked contrast the country underlaid by Ordovician 

 strata is prevailingly flat and fertile, well cleared, and 

 occupied by a large farming population. 



As shown by the accompanying geological maps, 

 the Laurentian country is underlain by a diversified series 

 of altered sedimentary rocks among which limestones 

 predominate, resting upon and invaded by enormous 

 bodies of gneissic granite. 



The sedimentary series is largely developed to the 

 south-east where it is comparatively free from igneous 

 intrusions. Towards the north-west, however, the granite, 

 in ever-increasing amount, arches up the sedimentary 

 series and wells up through it, in places disintegrating it 

 into a breccia composed of shreds and patches of the 

 invaded rock scattered through the invading granite, 

 until eventually connected areas of the sedimentary series 

 disappear entirely and over hundreds of square miles the 

 granite and granite-gneiss alone are seen, holding, however, 

 in almost every exposure, inclusions which represent the 

 last scattered remnants of the invaded rocks. The type 

 of structure presented by the invading granite is that of 

 a batholith. The term batholith is used in the sense in 

 which it was employed by Lawson in his classic work on 

 the Lake of the Woods and Rainy Lake districts, to desig- 

 nate great lenticular or rounded bosses of granite or gran- 

 ite-gneiss which are found arching up the overlying strata 

 through which they penetrate, disintegrating the latter, 

 and displaying at the same time a more or less distinct 

 foliation, which is seen to conform in general to the strike 

 of the invaded rocks when these latter have not been re- 

 moved by denudation. 



I. — The Invading Batholiths. 



The batholiths of the area are well shown on the 

 Bancroft sheet, and have a general trend in a direction 



