ANORTHOSITE-GABBRO IN NORTHERN NEW YORK 33 
An important feature, excluding the dikes below described, is 
the close association of facies very different in composition. In 
some cases such facies are asymmetrically arranged, but more 
commonly they are in the form of more or less well-defined belts of 
zones which in some cases show fairly sharp boundaries, though 
they mostly grade into the adjacent facies. Such belts or zones 
commonly vary from a fraction of an inch to some yards or rods 
wide. ‘The general effect is more or less well-defined local banded 
structures within the body of anorthosite-gabbro, especially in 
its northern portion. (See Fig. 2.) 
VARIATIONS IN FOLIATION 
Many portions of the anorthosite-gabbro, especially toward 
the north, exhibit more or less well-defined foliation. The greatest 
bulk of the rock is, however, practically devoid of such a structure. 
The non-foliated rock is mostly true gabbro, varying from light 
gray to very dark gray in color, medium grained to moderately 
coarse grained, generally with an ophitic texture. Some of the 
light-gray anorthosite-gabbro and anorthosite facies are also non- 
foliated. In many parts of the whole area there are gradations 
from facies which exhibit little foliation to others which are very 
highly foliated. As in the case of the variations in composition, 
so here the variations in degree of foliation generally occur as more 
or less well-defined belts or zones. Such belts commonly range in 
width from a few inches to some yards or rods. Highly foliated, 
moderately foliated, and non-foliated belts may lie adjacent to 
each other, in some cases with fairly sharp contacts, and in many 
cases with gradations from one into another. The variations in 
foliation are best exhibited in the northern portion of the area. 
In certain cases dark facies of the gabbro are so highly foliated that 
they look like hornblende schists. In other cases the rocks look 
like typical basic gneisses with alternating light and dark bands. 
Most of the anorthosite or gabbro shows moderate foliation due to 
a crudely parallel arrangement of the minerals, especially the 
dark minerals, without producing a banded effect. Figure 2 gives 
a fair idea of the variations in composition and foliation in a single 
small ledge. 
