FOLIATION IN THE PRE-CAM BRIAN OF NEW YORK 593 



panied by some crowding or squeezing of the Grenville between the 

 igneous masses, may have produced this very structure. Cushing 

 also argues that "the general parallelism of the foliation of all the 

 pre-Cambric rocks" affords "evidence of thoroughgoing compres- 

 sion of much later date" than the granitic intrusions. But, as will 

 be shown below, such parallelism of foliation is not necessarily 

 due to severe lateral compression. It should be said, however, 

 that in the Thousand Islands region the granitic and Grenville 

 rocks do seem to be more strikingly arranged in parallel northeast- 

 southwest belts than is usual throughout the Adirondacks. It is 

 possible that considerable orogenic forces did operate across the 

 area from the Thousand Islands region northward into Canada, 

 where also the parallelism is notable. Recent study of the Canton 

 quadrangle seems to indicate considerable folding there. Adams 

 and Barlow, in their description of the Haliburton and Bancroft 

 areas, state that the batholiths "are elongated or arranged in lines 

 having a prevailing direction of about N. 30 E., to which direction 

 the strike of the rocks (Grenville) lying between the batholiths in 

 general conforms. This direction constitutes, so to speak, the 

 general strike of the country, and shows that its present structure 

 has been determined, not only by the rise of granite magma, but 

 by the presence of a second factor in the form of a tangential 

 pressure, acting simultaneously." 1 But it is not at all certain 

 that this tangential pressure was really orogenic in character. 

 Even a very moderate compressive force, not at all sufficient 

 thoroughly to fold and plicate the rocks, acting upon the rising 

 magmas would readily account for all the structural phenomena 

 now visible. 



Variation of foliation strikes. — Even if we grant a very consider- 

 able lateral compression in the Thousand Islands-Canadian region, 

 the Adirondack area, fully a hundred miles across and to the south- 

 east, does not necessarily come under the same category. In fact, 

 while parallelism of syenite-granite and Grenville rock belts and 

 foliation are common in the Adirondacks, there are so many 

 important variations from a northeast-southwest strike that any 

 generalization regarding such a strike of the rock belts is of little 



1 Adams and Barlow, Geol. Sun. Can., Mem. 6, 1910, p. 16. 



