﻿Origin of the Grenvillc and Hastings Seriss. 305 



Laurentian" does not exist as an independent geological 

 series, the anorthosites, which were considered as con- 

 stituting its main feature, being in reality great intrusive 

 or batholitic masses ; while in a subsequent paper/ it was 

 shown that in the remaining portion of the Laurentian, 

 two distinct classes of rocks could be distinguished, the 

 first being beyond all doubt igneous rocks, and the second 

 consisting of highly altered rocks of aqueous origin. In 

 addition to these two classes of rocks of which the origin 

 could be recognized, there was yet a third class, concerning 

 the genesis of which there remained some doubt. 



Since the appearance of these papers, the present 

 writers have been working together in mapping a large 

 area (about 4,800 square miles) of the Laurentian in 

 •Central Ontario, comprising map-sheet No. 118, and a 

 portion of 119, of the Ontario series of geological maps, 

 the district lying to the north of Lake Ontario, along the 

 margin of the Protaxis, and being especially well suited 

 for purposes of study. Portions of three summers have 

 already been spent in the district, and as two years more 

 must probably elapse before the work can be completed, 

 it is desired here to present a general outline of the 

 results so far obtained, indicating certain conclusions 

 which seem likely to be reached concerning the origin of 

 the rocks in question. 



The Fundamental Gneiss, as shown by the work of the 

 Canadian Geological Survey, occupies by far the larger 

 portion of the protaxis as a whole; while the Grenville 

 Series has probably its principal development along the 

 south-eastern margin, although as the exploration of this 

 vast area is continued, new and possibly more extensive 

 areas of these rocks may yet be found. Strata, belonging 

 to this series, are already known to occur on the upper 

 Manicuagan Piver, the lower Hamilton Piver, on the 



1 Adams, F. D.— A Further Contribution to our Knowledge of the Laurentian, Am. 

 Journal of Science, July, 1895. 



