On the Norian or "Upper Laurentian" Formation. 293 



Kesume of the Kesults obtained from a Study of the 

 Morin Area. 



Tlie Morin area is a large eruptive mass of anorthosite, 

 that is to say, of a gabbro very rich in plagioclase. This 

 breaks through Laurentian rocks, and cutting off the differ- 

 ent members of the formation. It contains inclusions of 

 gneiss, sends out off-shoots into the gneiss, and is sur- 

 rounded in many places by a zone, which exhibits many 

 characteristics of a contact zone. The mass shows in 

 many places an irregular arrangement of the ingredients 

 and often variations in the size of grain, a peculiarity 

 often noticed in allied plutonic rocks. It exhibits, 

 moreover, a peculiar and unusual kind of cataclastic struc- 

 ture, which, where it occurs in a very marked manner, 

 induces a schistosity in the rocks. This structure is 

 caused by pressure, acting under peculiar conditions. 

 This schistosity is by no means a proof of an original sede- 

 mentary origin, and it is likewise evident that all 

 other arguments for the existence of a large independent 

 sedementary complex of which the anorthosite is supposed 

 to form part, are inconclusive. The gneisses and the lime- 

 stone with which it is said to alternate really belong to 

 the Grenville series, and the apparent interstratification 

 of the anorthosite is the result of intrusion. The anortho- 

 site, moreover, is unconformably overlaid by flat lying 

 unaltered beds of Cambrian age (Potsdam and Calciferous) 

 and, like the Laurentian rocks through which it cuts, must 

 have already possessed the characters which it now 

 exhibits in Cambrian times. 



III.— THE SAGUENAY AEEA. 



As far as we now know, the largest area of anorthosite 

 rocks is the one situated about the region of Lake St. 

 John, where the Saguenay river has its source. This river, 

 which is famous for the remarkable character of . its 

 scenery, flows throughout its whole course in a deep gorge; 



22 



