ANORTHOSITE-GABBRO IN NORTHERN NEW YORK 35 
VARIATIONS IN TEXTURE 
As already stated, most of the rock, except toward the north, 
is a true gabbro varying from gray to very dark gray, the latter 
predominating. Such gabbro is medium grained to coarse grained, 
and it commonly possesses a fair to excellent ophitic texture. In 
the northern portion of the area most of the rock is a gray to light- 
gray, medium-grained to moderately coarse-grained anorthosite- 
gabbro varying to anorthosite which does not so commonly possess 
an ophitic texture. Local zones of light- to dark-gray anorthosite- 
gabbro and gabbro throughout the area are fine grained to medium 
grained and generally more or less highly foliated. In some local 
portions of the general mass almost perfectly euhedral crystals of 
plagioclase up to an inch long are set in a fine, granular ground- 
mass of hornblende and monoclinic pyroxene. 
The great bulk of the dark-gray gabbro shows little or no 
granulation. The very light-gray anorthositic facies are commonly 
considerably granulated. Much of the white feldspar of the 
light-gray anorthosite-gabbro, especially in the northern portion of 
the area, shows more or less granulation. Non-foliated facies of 
the light-gray anorthositic gabbro exhibit little or no granulation 
of the dark minerals, but not uncommonly in the foliated facies 
the dark minerals as well as the feldspar are granulated. 
CAUSES OF THE VARIATIONS IN COMPOSITION, STRUCTURE, 
AND TEXTURE 
It is believed that most, if not all, of the foregoing variations 
in composition, structure, and texture are primary features, 
in other words, that they developed under conditions of moderate 
pressure before or during the final consolidation of the anorthosite- 
gabbro magma. ‘The main principles involved in the development 
of such features have been set forth by the writer in several recent 
papers' dealing with the origin of the foliation and banding of 
both the anorthosite and syenite-granite series of the Adirondack 
region. 
tW. J. Miller, Jour. Geol., Vol. XXIV (1916), pp. 600-619; Science, N.S., Vol. 
XLVIII (1918), pp. 560-63; Bull. Geol. Soc. Amer., Vol. XXITX (1918), pp. 399-462. 
