FOLIATION IN THE P RE-CAM BRIAN OF NEW YORK 617 



the degree of foliation varies much even well within single 

 stocks. 



Another very persistent feature is granulation which appears 

 to be of two types, that of so-called "corrosion rims" around certain 

 minerals, and a more generally distributed granulation. Granu- 

 lated "corrosion rims" occur even in non-foliated gabbro with 

 diabasic texture. 



Cause of foliation and granulation. — The foliation and granula- 

 tion of the gabbro, like that of the older intrusives, are quite gen- 

 erally regarded as secondary features brought about by the influence 

 of regional pressure, the non-foliated, uncrushed cores of stocks 

 being considered as portions protected from pressure influence. 

 Granting the existence of regional compression severe enough to 

 give rise to these phenomena, it is evident that the same pressure 

 must have affected the older intrusives in a similar manner, but 

 this we have proved to be not the case. It is very difficult to 

 imagine a process of development of foliation, which boxes the 

 compass around the borders of the gabbro stocks, by regional com- 

 pression. Such foliation of course often strikes directly across the 

 foliation of the older adjacent rocks, an excellent case in point being 

 at the south end of the large stock just north of Loon Lake of the 

 North Creek sheet. How can such phenomena be explained as 

 due to regional pressure when it is well known that cleavage or 

 foliation produced by this means must everywhere strike at least 

 approximately at right angles to the direction of application of 

 pressure ? Also how are such frequent notable variations in 

 foliat on and granulation, not on'y in near-by stocks but also 

 within stocks, to be explained ? 



According to the thesis of th's paper, the foliation and granula- 

 t on are largely, if not wholly, primary features. There are, 

 admittedly, some puzzling things about the foliation and granula- 

 tion of the gabbro, but certainly they are to be much more reason- 

 ably interpreted as caused by movements in the magma before 

 complete consolidation. 



Weinschenk, in explaining schistose peripheral zones around 

 certain Alpine granitic cores, has suggested: "The consolidation 

 of the rock commenced with the separation of the dark minerals^- 



