ANORTHOSITE-GABBRO IN NORTHERN NEW YORK 45 
to nearly white anorthosite relatively free from dark minerals, 
The ledge contains thousands of rounded to subangular pieces of 
medium to coarse granular plagioclase-rich material imbedded in 
a matrix of distinctly finer-grained groundmass. Remnants of 
the system of parallel curving cracks are clearly visible in parts 
of the ledge as, for example, just above the hammer in the picture 
(Fig. 7). Evidently here, as well as in that part of the ledge 
farther west, the system of crudely parallel curving cracks was 
developed by moderate pressure (probably a torsional strain) 
after the magma was nearly or completely solidified, but under 
continued pressure the rock was mostly shattered into small 
fragments. It seems likely that considerable nearly pure anor- 
thosite magma then invaded the shattered mass and that the 
rounding off of the fragments was probably partly due to the 
mechanical crushing and partly to magmatic corrosion. 
Certain other portions of the anorthosite-gabbro also show 
multiple fracturing but on lesser scales as, for example, at localities 
5 Wy Gaal Ty 
PEGMATITE DIKE RICH IN PYROXENE 
A pegmatite dike of special interest occurs in the anorthosite- 
gabbro at locality 3. It cuts across the foliation of the gabbro 
in the form of a lens with a length of twenty-five feet and a maxi- 
mum width of three feet. It sends off one distinct branch about a 
yard long into the gabbro. This dike consists mostly of feldspar 
(chiefly oligoclase) and green monoclinic pyroxene, together with 
5 to 8 per cent of quartz, all in anhedral crystals commonly from 
one to several inches long. Nearly all the pyroxene occurs in very 
irregular segregation masses up to several feet across. Some of 
the quartz is associated with plagioclase, and some occurs within 
the pyroxene segregation masses. ‘This dike lies in sharp contact 
against the anorthosite-gabbro except within a few feet of each end. 
This pegmatite is believed to be an offshoot from the adjacent 
granite, the magma or magmatic juices of which, on their way 
through the gabbro, dissolved or digested materials (chiefly ferro- 
magnesian) from the gabbro, thus giving rise to the rather basic 
pyroxene-rich pegmatite. Because of the dissolving power of the 
