38 NEW YORK STATE MUSEUM 
greatly disturb the continuity of strike of the gneiss. In cases of 
more complete assimilation there was still failure in the uniformity 
of redistribution of the different matters so that much of the 
streaked and banded structure may be a sort of preservation of the 
original structure of the rocks absorbed, and may be called, therefore, 
an antecedent structure **; a structure crudely preserved after the 
rock which it represents has been otherwise almost wholly destroyed. 
Subsequent intrusion by additional igneous matters has complicated 
the situation, but, while it is probable that more or less deformation 
occurred during the intrusion of the several igneous masses in Pre- 
cambrian times, the crystalline rocks of the Highlands as a whole 
seem to have passed through both the Appalachian and Taconic 
revolutions without marked folding, and to have been affected only 
in so far as thrust faulting of the Appalachian type would indicate. 
The causes of the complexity and variable habit of the crystalline 
rocks of the Highlands may then be ascribed to: (qa) Original 
differences in composition of the metamorphosed Grenville sediments 
which form the basis of the gneisses; (b) original differences in the 
composition of the several invading magmas; (c) magmatic differ- 
entiation within these magmas, with movement and development 
of flow structure; (d) syntexis, both partial and complete; (@) 
igneous impregnation, as distinguished from mere /it-par-lit injection ; 
(f) lt-par-lit injection of magmatic material; (g) contact effects; 
(h) shght deformation during the invasion of the Pochuck magma 
and subsequent faulting, both Appalachian and Triassic. 
Berkey °*’ found, during his studies of the Highlands geology, 
that certain of the magmatic units were exceptionally capable of 
invading the surrounding country rocks in such an insidious and 
petvading way as to penetrate all weaknesses, producing lit-par-lit 
injection effects, and also to assimilate much rock. Both the 
Pochuck granite (see part 3) and the Canada Hill granite are 
representatives of this type. Other invading magmas were appar- 
ently less capable of assimilating, so that xenoliths resulted. The 
Storm King granite is representative of the latter type. This 
interpretation makes it possible to recognize several magmatic units 
separable on the basis of unity of origin, like structural or field 
relations and petrographic constancy. 
82 Berkey, C. P., & Rice, Marion. Geology of the West Point Quadrangle. 
N. Y. State Mus. Bul. 225-26. 
°3 Personal communication. 
