THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 29 



parallel belts of garnet gneiss, and leave unchanged between them 

 a layer of normal crystalline limestone identical with that from 

 which the contact hypothesis would suppose the aureole to have 

 been produced. 



If, however, the contact theory is ruled out, it is necessary to find 

 a more satisfactory explanation for the remarkable distribution of 

 this belt of garnet gneiss. It seems not unreasonable to suppose 

 that previous to the crustal deformation which has produced such 

 wholesale contortions among the Grenville rocks of this vicinity, the 

 garnet gneiss flanking the west side of the reentrant was continuous 

 with that which borders the east side, and that the formation was 

 continuous eastward to Little River. Tectonic disturbances, coupled 

 with the effects of the local introduction of a bulky half sill-like, 

 half bosslike body of granite, would seem co be competent to ac- 

 count for the present distribution of the formation. The granite 

 was intruded previous to, and probably also in large part during, 

 the period of folding, at the horizon of the upper contact of this 

 stratum of garnet gneiss, which has accordingly played the role of 

 foot wall, except where overturning, as at the head, and on the 

 southeast side, of the reentrant, has locally transformed it into the 

 roof of the granite. It would appear that as the compression of the 

 area continued, and the volume of magma squeezed into it at this 

 horizon increased, the granite assumed a bluntly lenticular or sub- 

 circular form, which it was permitted to do by reason of the easy 

 plasticity and nonresistant character of large masses of surround- 

 ing limestone. Where the garnet gneiss had a local tendency to 

 bulge away from the granite, the viscous magma evidently seized 

 upon the incipient flexure as a point of weak resistance, and, accen- 

 tuating the deformation, occupied all the available space with its 

 own substance. The garnet gneiss throughout the whole process 

 has shown almost as much plasticity as the adjacent limestone and 

 compressed between the granite gneiss on one side and the lime- 

 stone on the other, has yielded to the deformative forces by a 

 moderate amount of stretching and thinning. If it has broken at 

 all, the fractures occurred at the east and near the west ends of the 

 boss, and crystalline limestone, because of its lesser competency, 

 has flowed in between the separated parts. 



As to the origin of the garnet gneiss in the second case cited, 

 those masses bordering the east and west extremities of the body of 

 granite southwest of Pyrites, it is probable that the same interpre- 

 tations must be accepted as in the case above described. The failure 

 of the rock to form an uninterrupted zone round the granite^ its 



