1893. | NEW YORK ACADEMY OF SCIENCES. 211 
so abundant as to make them true tourmaline granites. Another 
phase, which has been distinguished as granulite* (perhaps 
unfortunately, as it lacks the foliation of a typical granulite), 
occurs at many points. It is fine grained and white, resembling 
sandstone. Under the microscope it is seen to be a mosaic of 
quartz and feldspar, with numerous larger individuals of garnet. 
There is wide variation in the character of the feldspar, but 
microcline is often conspicuous. 
The garnet usually shows crystal outlines, though irregular 
grains are also present. It has a decided pink color and inclu- 
sions are abundant. These have, as a rule, the shape of nega- 
tive crystals, and are more or less concentrated toward the 
centers of the crystals. With the exception of some apatite 
and zircon, other minerals are lacking. The field relations of 
the granulite and ordinary granite show a perfect continuity 
between the two rocks, and suggest that the two varieties are 
due to a differentiation of the original magma. But under the 
microscope the granulite shows a marked cataclastic structure, 
together with a large amount of secondary quartz and feldspar. 
Tt has clearly been formed from the ordinary granite by the 
shattering of the constituents of the latter rock, attended by a 
large amount of recrystallization. 
In one portion of the granitic area there are several alterna- 
tions between the ordinary granite and a very dark rock com- 
posed of hornblende, biotite and plagioclase—a quartz-free 
diorite in composition, though lacking the structure of a typical 
diorite. The passage from the ordinary granite to this dioritic 
variety is very gradual, there being no break whatsoever between 
them, and there can be no doubt that the diorite is a basic 
segregation from the original magma. 
The effects of dynamo-metamorphism upon the granite, while 
almost always apparent, are not, as arule, very conspicuous, The 
bending, stretching and crushing of minerals have been men- 
tioned, but these effects are generally to be seen only with the 
aid of the microscope. Small areas of the rock, however, often 
show incipient foliation, and at some outcrops the granite 
passes into a true gneiss, which is, however, entirely distinct 
from the older gneiss previously described. The formation of 
granulite has already been mentioned. As to why the granite 
sometimes changes to gneiss and sometimes to granulite, there 
is no very clear evidence. But comparison of sections of the 
two varieties indicates that the granulite results from a more 
complete shattering of the granite, to which, with the absence 
* Trans, N. Y. Academy Sciences, XII., p- 105. 
