FOLIATION IN THE PRE-CAM BRIAN OF NEW YORK 601 



Northeast-southwest structure of rocks. — We have shown that the 

 Grenville series has never been closely folded or severely com- 

 pressed, and that its foliation was not caused essentially by lateral 

 pressure. The syenite-granite masses, being younger than an 

 intrusive into the Grenville, cannot, therefore, have had their 

 foliation developed chiefly by lateral pressure, though the probable 

 existence of a very moderate lateral pressure is admitted. 



In spite of many important exceptions, there is some tendency 

 toward a general parallel northeast-southwest to east-west strike 

 of Adirondack rock masses (Grenville and syenite-granite) and 

 foliation. One view, clearly stated by Cushing, is that "since the 

 rock [granite] solidified it has been subjected to compression, to- 

 gether with the Grenville rocks, giving to each a foliation parallel 

 to the other, and elongating the batholiths in a northeast-southwest 

 direction." 1 At another place he refers to this compression as 

 "thoroughgoing" and of much later date than the granite intrusion. 

 Cushing suggests the possibility of the development of "a similar 

 and parallel foliation" 2 during the solidification of the batholiths 

 due to their shouldering pressure exerted upon the adjacent rocks 

 during the intrusion, but he says that if any such foliation de- 

 veloped it was obliterated by subsequent compression. 



The writer's view is that the general northeast-southwest 

 structural parallelism was brought about by just enough tangential 

 compression to control the general directions of the upward- 

 moving batholithic magmas. Accordingly, the intrusive bodies 

 were more or less elongated during the process of intrusion, and 

 there must have been a strong tendency for large and small bodies 

 of previously horizontal, or only slightly deformed, Grenville 

 strata to have been caught up and arranged with their long axes 

 and foliation parallel to the magmatic currents, while the foliation 

 of the intrusives would also have developed, as a sort of flow struc- 

 ture under moderate pressure, parallel to the magmatic currents. 

 This pressure was doubtless in part due to the shouldering effect 

 of the intrusives upon the adjacent rocks. In other words, the 

 syenite-granite gneisses are "primary gneisses." Thus we should 



1 H. P. Cushing, New York State Mus. Bull., No. 145, 1910, p. 10. 



2 Ibid., No. 145, 1910, p. 102. 



