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The Pre-Carboniferous strata, at first considered to 

 represent metamorphosed Carboniferous measures intruded 

 by granitic bodies, were next thought to be of Silurian 

 age, and finally, by Fletcher were mapped and described 

 as divisible into Lower Silurian (i. e. Cambrian) and 

 Pre-Cambrian. Later still Matthew subdivided the 

 Cambrian into five divisions and placed in the Cambrian 

 certain strata previously considered to be of Pre-Cambrian 

 age. 



The Pre-Cambrian strata as mapped by Fletcher, 

 occupy by far the larger part of the area of the Boisdale 

 hills. The Carboniferous beds occur only in the form of 

 a narrow, discontinuous border. The Cambrian beds are 

 mainly confined to a long, narrow zone which in the north 

 forms the western margin of the upland but in the south, 

 extends from side to side of the Pre-Cambrian area. 



The Pre-Cambrian was divided by Fletcher into two 

 groups. One of these was termed the George River series 

 and because of its lithological characters was supposed 

 to be the equivalent of the Grenville-Hastings series of 

 Quebec and Ontario. This view was adopted by Matthew 

 also. As described by Fletcher, the George River series 

 consists of crystalline limestone, quartzite, mica schist, 

 hornblende schist, etc, interleaved with granitic and 

 gneissic rocks. The strata in most places, are inclined 

 at high angles and are highly metamorphosed. The 

 series was regarded as essentially of sedimentary origin 

 and was believed to be younger than, and to rest uncon- 

 formably on the associated granitic rocks. This view 

 of the relations existing between the sedimentary series 

 and the plutonic rocks was doubltess based on the beliefs, 

 held in the 70's at the time the field work was performed, 

 regarding the relations existing in the typical Laurentian 

 areas of Quebec. Recent examinations made of some 

 typical sections of the George River series indicate, how- 

 ever, that the granitic rocks unmistakably cut and are 

 younger than the George River series. The correlation 

 on lithological grounds of the George River series with the 

 Laurentian (Grenville-Hastings) of distant Quebec is 

 perhaps no longer justifiable. But the various points 

 of resemblance existing between the Pre-Cambrain of 

 Cape Breton and the original Laurentian, are worthy of 

 note. 



