THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 73 



of the country rock, especially where the granite was locally more 

 abundant, may have been, and undoubtedly were, partially or wholly 

 rnelted by the intrusive, and were thus actually absorbed or assimi- 

 lated by the granite magma, upon which they exerted a chemically 

 modifying influence. On the other hand, at certain points, as typi- 

 fied by plates ii, lower figure, and 13, upper figure; the admixture 

 may have been of a purely physical character, with little or no 

 chemical absorption of the country rock. Indeed, the widespread 

 graduation from coarse-textured to fine-textured injection gneiss 

 lends support to this view, and in such cases as that now instanced, 

 where the minerals foreign to the granite are those normal to the 

 amphibolite, and vice versa, it is thought that a mere mechanical 

 insinuation of the acidic magma into, and its intimate permeation 

 through, the hornblendic country rock without implied melting or 

 absorbtion of the latter, is a possible explanation of the thorough ad- 

 mixture of the two types. How far this cause may have been 

 effective in particular cases, however, it is useless to speculate ; 

 though it appears to have been dominant in the case cited, it may 

 have been negligible in others. 



Thus far the igneous character of the large areas of granite gneiss 

 in the western half of the sheet and of the injection granite in the 

 southeastern corner has been taken for granted. It will be of inter- 

 est, however, briefly to point out the basis for this assumption, and 

 to indicate the character of the available evidence as to the relative 

 ages of the acid and basic intrusives. Conclusive and localized 

 phenomena demonstrating the intrusive nature of the granite gneiss 

 with respect to the Grenville can seldom if ever be obtained in this 

 vicinity. Widespread regional metamorphism has produced a gen- 

 eral banding or foliation in all the formations involved, and has 

 reduced transgressive contacts, if such existed, to parallelism with 

 the secondarily superimposed schistosity. Accordingly all bodies 

 of granite, whether originally concordant or discordant with their 

 country rock, appear now at the exposed contacts as interbanded 

 masses. Thus, the broad belt of granite which extends through 

 Canton village and the two more nearly circular masses in the neigh- 

 borhood of Pyrites, are overlain and underlain at the present sur- 

 face of erosion by Grenville schists and limestone, and the evidence 

 at the exposed contacts is therefore inconclusive as to whether the 

 granite is interbedded or intruded, of sedimentary or igneous origin. 



