32 ROY A L SOC 1 KTY OF CAN A DA 



dilTiculty at present appears to be tlie assigning of certain portions of 

 these apparently newer masses to their proper iiorizon. Tims if we as- 

 sume that these intrusive and igneous rocks were originally portions of 

 the first formed crust, which have penetrated through the overlying 

 gneissic portions, two views may he adopted, viz., either these may also 

 be called Laurentian, regarding them as the equivalents in origin with 

 the rocks of the oldest crust, from which they have been extruded, or 

 they may be regarded as newer than the rocks which they penetrate, 

 their classification being based on the time of their intrusion. 



In the case of certain intrusive or igneous rocks, whicli are now 

 found in association with the porticn styled Grenville and Hastings 

 series, some of these are undoubtedly assignable to a newer position, as 

 has been done in the case of the anorthosites and some kindred rocks, 

 and these have, within the last few years, been entirely separated from 

 the rocks of the so-called Laurentian system, since they cut the lime- 

 stones and gneiss of that series. Illustrations of this feature of in- 

 trusion may be observed in the mass of syenite and granite of Grenville. 

 These rocks must, however, have had their origin from some portion of 

 the original magma beneath the upper gneiss wdiich they penetrate, and 

 as such would seem to represent a portion of the Laurentian proper. In 

 the eastern part of Quebec, as also in Xova Scotia and in New Brunswick, 

 there are large areas of similar looking granite which penetrate rocks of 

 pre-Cambrian, Cambrian, and other formations as high as the lower part 

 of the Devonian. These have doubtless been exposed by denudation of 

 the sedimentary beds of these districts, and they presumably had their 

 origin in the same manner as those which cut the cr3^stalline rocks of 

 Grenville. They have not, however, in general been regarded as Lauren- 

 tian but as newer intrusives; and their age has usually been considered 

 to be that of the newest rocks which they penetrate. 



In the study of the Ottawa district, it is found, that as we go north- 

 ward from the Ottawa Eiver towards the height of land, the overlying 

 .series of gneiss and limestone becomes greatly reduced in volume, and at 

 last apparently disappears entirely in many places, while the country in 

 this direction becomes occupied largely by the lowest or Fundamental 

 gneiss and granite. In this case also there can be no apparent reason 

 why these old rocks may not with propriety be placed in the Laurentian. 

 In the area nearer the Ottawa, and in that portion of Ontario to the 

 south, portions of this oldest gneiss appear at intervals from beneath the 

 newer series of crystallines, and these would seem to be exposed by the 

 denudation of the latter. Over long distances all these rocks are now 

 thrown into a succession of folds with occasional overturns, in which the 

 anticlines run in a generally north and south direction. The anticlines 



