THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 33 



lithologic transitions, if such exist, are nowhere exposed; the proxi- 

 mate country rock is never, so far as is known, a normal or even an 

 impure Hmestone, but is generally a (garnetiferous) mica schist. 

 Accordingly the evidence as to the garnet amphibolite being a con- 

 tact rock may in this case be held in question, though the limited 

 parallelism with the occurrence east of Pyrites, and the notable 

 peripheral distribution, are points in its favor. 



The problem of the chemical method by which an acid granite 

 unusually low in femic constituents may transform a carbonate 

 rock into a highly ferromagnesian amphibolitic end-product is dis- 

 cussed at some length by Adams and Barlow (1910, pages 87-115) 

 and need not be described here. If, however, the general trans- 

 fusion of the iron and magnesia molecules from the acid magma to 

 the country rock and their fixation in adjacent limestone be admitted 

 as a possible method for the derivation of the peripheral and con- 

 tained amphibolites, then the present instances are good illustra- 

 tions of this process. Furthermore in the Eddy vicinity it must be 

 conceived to be applicable to the alteration of micaceous, garnet- 

 bearing schists into amphibolite end-products similar to those ob- 

 tained when limestone is the country rock; unless at Eddy, as is 

 very unlikely, the intergranite schist area north of this village is 

 itself assumed to be a phase of an unusually broad and extensive 

 contact zone formed against an original limestone body whose rem- 

 nants now appear as a comparatively unaltered residuum in the two 

 small calcareous patches north of the village. 



As already intimated, the question as to the possibility of this 

 garnet-bearing formation being a transitional contact rock is not 

 easy to decide from the data obtainable. The crenulations in this 

 area of Grenville undivided gneisses are so intense and so irreg- 

 ular that it would be taking much for granted to assume that the 

 garnet gneiss and its accompanying amphibolite form a definite 

 horizon along which the granite happens to have been intruded. 

 This interpretation, moreover, is not supported by the same circum- 

 stantial evidence that lends probability to the initial sedimentary 

 origin of the garnet gneiss which half surrounds the boss east of 

 Pyrites. In the Eddy vicinity the constant association of the garnet 

 rock with a black amphibolite interposed between it and the granite 

 would seem to be more than accidental, and the view that it is a 

 contact zone intermediate between the unchanged biotitic schists 

 and the extreme of alteration, amphibolite, is strongly suggested. 



From a point about 2 miles east-northeast of Eddy to the 

 village of Canton, the border of the granite can not be observed to 

 be accompanied by this association of amphibolite and garnet gneiss. 



