CURRENT PRE-CAMBRIAN LITERA TURE 4 I 3 



anorthosite upon the Laurentian gneisses, which have been carefully 

 investigated, the unconformability is found to be due to intrusion. 



9. The anorthosites are probably of pre-Cambrian age, and seem 

 to have been intruded about the close of the Laurentian. 



10. The Canadian anorthosites are identical in character with the 

 anorthosites associated with the Archean rocks of the United States, 

 Norway, Russia, and Egypt. The Norwegian occurrences, however, 

 are probably more recent in age than those of Canada. 



Adams and Barlow 1 give a general outline of geological work 

 begun, but not yet finished, in the Laurentian of central Ontario, in 

 the area comprising map sheets No. 118 and a portion of 119 of the 

 Ontario series of geological maps, and indicate certain conclusions 

 which seem likely to be reached concerning the origin and relations 

 of the Grenville and Hastings series. 



The Fundamental Gneiss occupies the northwestern, and by far 

 the larger portion of the area. It consists of igneous rocks closely 

 allied to granites, diorites, and gabbros, all showing more or less 

 distinct foliation. 



The Grenville and Hastings series are principally exposed in the 

 southeastern portion of the area, the Grenville series appearing in a 

 belt adjacent to the Fundamental Gneiss, and between the Funda- 

 mental Gneiss and the Hastings series. 



The Grenville series is composed principally of gneisses identical 

 in character with the Fundamental Gneiss, but it contains also, and is 

 characterized by a small quantity of altered sediments, chiefly lime- 

 stone. Some varieties of the gneissic rocks may owe their origin to 

 the partial commingling of the sedimentary material with the igneous 

 rocks by actual fusion. The strike of the foliation of the rocks of the 

 series follows in a general way that of the Fundamental Gneiss. The 

 Grenville series is believed to be a sedimentary series, later than the 

 Fundamental Gneiss, which has sunk down into, and been invaded by, 

 intrusions of the latter series when this was in a semi-molten or plastic 

 condition. 



The Hastings series is composed chiefly of thinly bedded lime- 

 stones, dolomites, etc., cut through by great intrusions of gabbro, 

 diorite, and granite. This series is believed to represent the Grenville 



'On the origin and relations of the Grenville and Hastings series in the Canadian 

 Laurentian, by F. D. Adams, and Alfred E. Bari.ow: Am. Journ. Sci., 4th ser., 

 Vol. Ill, 1897, pp. 173-180. 



