166 F. D. ADAMS—NODULAR GRANITE FROM PINE LAKE, ONTARIO. 
from this and numerous other observations that these “ veins” do not 
represent merely single lines of nodules, but rather sheets which fray out 
into separate nodules along their outer margins. 
Whether irregularly disseminated through the rock, as is usually the 
case, or whether arranged in lines or sheets, as in certain rare instances, 
the nodules bear a striking resemblance, so far as mode of occurrence is 
concerned, to the spherulites, axiolites, and other similar structures seen 
in obsidian and other volcanic rocks, although, of course, on a very much 
larger scale (see plate 11, figure 2). 
The several structures described can be duplicated on a small scale in 
many hand specimens of the obsidian from the Yellowstone park. The . 
_ presence of tourmaline and muscovite is suggestive of the presence of 
mineralizers, which also play so important a part in the formation of 
spherulites. ‘These nodules, however, differ in a marked manner from 
such spherulites in that their composition is not identical with that of 
the enclosing rock, while in the case of the spherulites there is a practi- 
eal identity in this respect. That an abundance of mineralizer was 
present in certain parts of the granite magma is, however, indicated by 
the streaks or more or less irregular segregations of coarsely crystalline 
quartz and tourmaline found in places through the rock. 
MicroscopicAL CHARACTER OF THE ENCLOSING GRANITE 
The red granite from various parts of the area is found when examined 
under the microscope to be uniform in composition and microscopical 
character, although, as has been mentioned, varying somewhat in grain. 
Orthoclase and microcline preponderate largely, the former in untwinned 
grains, showing good cleavages, the latter presenting a well marked cross- 
hatched structure. Soda-lime feldspars are also present, although in 
very subordinate amount. The microcline, which is usually about equal 
to the orthoclase in amount, is in some places present in large grains with 
irregular boundaries and a marked micropoikilitic structure, the enclosed 
erains consisting of orthoclase, plagioclase, and quartz, with a few of bio- 
tite and iron ore. ‘These inclusions, which are often very numerous, are 
more or less rounded in form, their outline being often nearly circular. 
They are also quite irregularly oriented. The microcline in these cases 
is evidently younger than the other constituents of the rock, with the 
possible exception of the quartz, as has been found to be the case with 
this mineral in a number of granites which have been recently studied. 
The quartz is much less abundant than the feldspar and often occurs 
in subpolygonal or more or less rounded grains, instead of occupying 
the interstices between the other minerals as in a normal granite, a mode 
of occurrence which marks an approach in character to that seen in the 
