﻿Origin of the Grcnvillc and Hastings Series. 315 



ill the intrusive nature and later age of many of these 

 masses, while the aid of the microscope fully established 

 the non-clastic and igneous cliaracter of the great bulk of 

 the gneisses. The more recent and probably sedimentary 

 origin of the limestones and associated gneisses of the 

 Grenville series, as distinct from the great mass of the 

 underlying Laurentian Fundamental Gneiss, was pointed 

 out some years ago in a paper by the author, read before 

 the Geological Society of America. The subsequent 

 investigations on tliese rocks, to the west and south-west, 

 showed that the conclusions then presented were correct, 

 but that as the work extended westward to the south side 

 of the Ottawa the character of the various groups of rocks 

 gradually changed. The areas of limestone became much 

 more extensive, and there was a large development of 

 hornblende and other dark-colored rocks, rarely seen 

 to the north of the Ottawa. The limestones also were 

 very often highly dolomitic, and in certain areas were 

 blue and slaty, with but little of the aspect of the 

 Grenville limestones, except where they were in close 

 contact with masses of intrusive granite or diorite. 

 There is also in the rocks of this group to the south of the 

 Ottawa, where they have been styled the Hastings series, 

 from the fact that they were first studied in the county of 

 Hastings, a very considerable proportion of schists, 

 micaceous, chloritic and hornblendic, with certain regu- 

 gularly slaty beds, and others of true conglomerate 

 containing quartz pebbles. In certain portions the 

 lithological resemblances between the Grenville and 

 Hastings rocks are very close, and they may, for all 

 practical purposes, be regarded as one and the same series. 

 From a number of sections made in the counties of 

 Eenfrew on the south of the Ottawa, and in Pontiac, 

 to the north of that river, it would appear that the 

 original Grenville limestones and associated grey and 

 rusty gneiss from the lower part of the series, since it is 



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