FOLIATION IN THE PRE-CAMBRIAN OF NEW YORK 615 



or inclusion and consequent development of differential pressure 

 and flowage, so, on a large scale, in the anorthosite body it is 

 reasonable to think that foliation due to magmatic flowage would 

 have been best developed around the margin of, or close to, masses 

 of country rock within the great anorthosite body. In many 

 other places, however, primary gneissoid structures may have been 

 produced by differential flowage far from any country rock. 



The cataclastic texture of the anorthosite is believed to have 

 resulted from the crushing of minerals already crystallized out of 

 the stiff, solidifying magma by movements in the magma. The 

 shouldering pressure exerted by the great intrusive mass in order 

 to make room for itself must have been sufficient to have affected 

 the whole mass until final consolidation. 



Kemp says, regarding the anorthosite of the Elizabethtown 

 quadrangle: "The entire area has been subjected to such severe 

 pressure and granulation that the outer borders of the crystals 

 are always crushed to a finely granular and whitish mass. Within 

 this rim the bluish nuclei of the plagioclases remain. When shear- 

 ing and dragging have been added the nuclei yield augen-gneisses." 1 

 It is, however, not at all necessary to assume severe regional pres- 

 sure to account for these phenomena. Forced differential flowage 

 in the stiff, nearly congealed magma (under pressure due chiefly 

 to its own shouldering action) could have produced most, if not all, 

 of the granulation and dragging effects, the "augen" being cores 

 of what were large, probably porphyritic, feldspars in the nearly 

 solidified magma. Moderate pressure during or even after con- 

 solidation may possibly have operated to accentuate the phenomena. 



Adams says, concerning the Morin anorthosite north of Mon- 

 treal: "The circumstance that the streaks or irregular bands 

 (foliation), when present in the otherwise massive rock, assume no 

 definite direction, but twist about as if owing to movements of 

 the rock while in a pasty condition, indicate that they have been 

 produced by movements before the rock solidified The granu- 

 lation of the coarsely crystalline massive anorthosite, usually with 

 concomitant development of more or less foliated or schistose 

 structure in the way described, is undoubtedly due to movements 



1 J. F. Kemp, New York State Mus. Bull., No. 138, 1910, p. 28. 



