﻿130 • PROF. r. DAWSON ADAMS ON THE [Mav I908, 



will appear elsewhere, and reserving also the detailed description 

 of the area itself for a Eeport which wi]l be published bj^ the 

 Geological Survey of Canada during the present year (1908). 



II. Structttiie or the Area. 



A cursory inspection of the accompanying map (PI. XIII) will 

 show that, geologically speaking, this Laurentian country is underlain 

 by a diversified series of stratified rocks (Grenville Series), among 

 which limestones preponderate, resting upon and invaded by an 

 enormous body of gneissic granite. 



To the south-east the sedimentary series is largely developed,, 

 and 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 dis- 

 integrating 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 

 bathylith. In the present paper, the term bathylith is used in 

 the sense in which it was employed by Prof. Lawson in his 

 classic work on the Lake-of-the- Woods and Eainy-Lake districts of 

 Canada, to designate great lenticular or rounded bosses of granite 

 or granite-gneiss which are found arching up the overlying strata 

 through which they penetrate, disintegrating the latter, and 

 possessing 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 removed by denudation. 



III. The Invading Bathtliths. 



The bathyliths of the area are well shown on the Bancroft sheet 

 and have a general trend in a direction about N. 30° E., which is 

 also the direction in which the area is folded. They are in some 

 cases isolated occurrences ; in other cases they occur in linear series 

 so constituted, that it is evident that a very small amount of addi- 

 tional erosion, by removing the intervening cover, would convert the 

 series into a single long narrow bathylith. 



Within the area of the bathyliths themselves the strike of the 

 foliation follows sweeping curves, which are usually closed and 

 centred about a certain spot in the area where the foliation becomes 

 80 nearly horizontal that its course and even its existence, where 

 the surface is level, becomes difficult to recognize. Prom these 

 central areas of flat-lying gneiss, the dip of the gneiss (where it can 

 be determined) is usually found to be outward in all directions. The 

 bathyliths are. therefore, undoubtedly formed by an uprising of the 



