268 



The George river series as mapped by Fletcher is confined 

 to three, long, detached areas situated along the south- 

 eastern flank of the Boisdale hills. These areas border 

 the great central mass of the ranges regarded by Fletcher 

 as essentially occupied by granite but including large and 

 small areas of rocks that in some cases possibly belong to 

 the George River series and in others to the Cambrian. 

 As already stated, it is now advocated that the granitic 

 rocks are younger than the George River series. It is 

 assumed, therefore, that the Pre-Cambrian of the Boisdale 

 hills consists of the remnants of one or more series of 

 limestones, quartzites, etc., and possibly deformed 

 volcanics, intruded by bodies of granitic rocks. In the 

 extreme northern portion of these hills, the granites form 

 relatively large, homogenous areas from which offshoots 

 extend into the older, bedded series. 



The Pre-Cambrian age of the above described assemblage 

 of strata has been established by Fletcher, who stated that 

 Cambrian conglomerates hold rock fragments similar to 

 varieties of rocks in the Pre-Cambrian, and that the Cam- 

 brian is nowhere cut by the granites. Examples of the 

 actual unconformable superposition of the Cambrian on 

 the Pre-Cambrain have been described by Fletcher and 

 Matthew. In general, however, the two rock groups are 

 in contact along faults. 



The Cambrian measures as mapped by Fletcher, form a 

 long, narrow band extending nearly the whole length of the 

 Boisdale hills. As described by Fletcher, the Cambrian 

 consists of a series of sediments and, also, a group of 

 igneous rocks generally described under the name of 

 'felsites.' On an earlier map, a considerable area of these 

 igneous rocks is unquestionably included in the Cambrian. 

 On a later map, a portion of these igneous rocks is mapped 

 separately. The relation of these igneous rocks to the 

 Cambrian sediments is not specifically described by 

 Fletcher, nor is it very apparent on what grounds certain 

 'felsites' were mapped as Cambrian while others were 

 assigned to the Pre-Cambrian. Matthew has definitely 

 grouped certain of the igneous rocks with the Cambrian, 

 including some that by Fletcher were considered Pre- 

 Cambrian. 



Matthew has subdivided the Cambrian, on paleonto- 

 logical and lithological evidence, into five groups. The 



