On the Norian or " Upper Laurentian " Formation. 181 



west of the anorthosite (for he investigated only this 

 region) Logan found that two of the limestone bands, 

 one on the southwest and one farther north on the west 

 side of the area, were cut off by the Morin anorthosite, 

 and he therefore considered the latter as a newer forma- 

 tion which overlay them, observing that in case it should 

 be proved (by an extension of the observations farther 

 to the north than it was possible for him to carry them) 

 that two other limestone bands which he had followed up 

 nearly to the limit of the anorthosite were likewise cut 

 off by it, this fact might be considered as conclusive evi- 

 dence of the existence of an Upper Laurentian series 

 reposing uncomformably on the Grenville series. A care- 

 ful investigation of this northwest corner of the area which 

 was undertaken last summer, in company with Dr. Ells of 

 the Geological Survey, showed, however, that one of the sup- 

 posed interruptions really does not exist and that the drift 

 is so heavy in this region that even if the other limestone 

 stone bands do come against the anorthosite, the contact 

 could not be observed. A careful examination of the con- 

 tact on the southwest corner of the area in the neighbor- 

 hood of the village of St. Sauveur, however, leaves little 

 doubt that the limestone is really cut off by the anortho- 

 site at this point. The limestone underlies a plain and 

 protruding here and there in large exposures through the 

 drift, whilst the anorthosite rises from this plain as a steep 

 wall or cliff. The limestone is exposed 200 yards from the 

 foot of the anorthosite wall, but the drift covering then 

 becomes so thick that the character of the contact itself 

 cannot be determined. Both to the east and to the west, 

 the associated gneiss is cut off in a similar manner. 



On the northeast side of the anorthosite area there was 

 found, moreover, another limestone band which runs 

 through Lake Ouareau aud forms in it a series of small 

 islands. It is also well exposed on the south shore of this 

 sheet of water. This bed disappears at the edge of the 

 anorthosite a short distance from the south end of the lake, 

 and no further traces of it are seen until it appears again 



