[alcock] granite on CHURCHILL RIVER 33 



Cutting this dyke are two sets of pegmatite. The younger is 

 slightly the coarser grained, but both are light coloured and consist 

 of feldspar and quartz with but very minor amounts of ferromagnesian 

 minerals. 



The relationships are suggestive of a common origin for all the 

 varieties from the same parent magma. If the pegmatites are the 

 final products from the magma which produced the regional granite, 

 the dark hornblende rock must be a differentiate of a slightly earlier 

 stage. The conclusion is, therefore, that the local differences in 

 composition and structure are due to differentiation and that it is not 

 necessary to postulate successive intrusions of granite of various 

 ages. It also emphasizes the fact that caution should always be used 

 in the separation of granites where there are no sediments to estab- 

 lish their relative ages. 



Sec. IV. Sig. 3 



