172 F. D. ADAMS—-NODULAR GRANITE FROM PINE LAKE, ONTARIO. 
rious incipient crystal forms, as shown by Vogelsang and others in their 
experiments on the crystallization of sulphur. Any very small isolated 
schlieren that were developed through the magma or detached from the 
larger schlieren by movements in the semifluid mass would, of course, 
without encountering much resistance, take upon themselves a globular 
form, while in the case of larger streaks and sheets more resistance would 
be offered by the stiffness of the magma and the tendency to assume a 
elobular form would be less pronounced. 
When the magma had cooled sufficiently and crystallization began to 
set in, the solidification in the case of the granite followed the usual 
course, while the schlieren and globules, having a marked difference in 
composition, gave rise to different mineral combinations, and at the same 
time, perhaps on account of their peculiar chemical composition or per- 
haps because they contained a greater proportion of mineralizers, they 
developed during crystallization a tendency to spherulitic arrangement. 
In the case of the separate nodules, the crystallization seems to have 
started from the center and to have proceeded outwards, and, toward the 
extremity of the schlieren, to have commenced at a series of points along 
the medial line. The medial line of the schlieren thus corresponds to 
and is identical in character with the central portions of the nodules. 
The possibility of the nodules having been produced by the melting 
down of portions of some fibrolitic band in the wall rock is eliminated 
by the fact that not only are such bands not found in the wall rock, this 
being everywhere a basic gabro-like amphibolite entirely different from 
the nodules in composition and character, but also by the zonal arrange- 
ment often observed in the nodules and their passage into the indistinctly 
banded vein-like forms which, as before mentioned, in some cases divide 
and fork, and are thus clearly not portions of the wall rock. 
Whether any of the quartz veins so commonly found associated with 
granitic gneisses of undoubted igneous origin in the Archean or the 
quartz veins and strings, often rich in sillimanite, found abundantly in 
the altered rocks surrounding certain great granite intrusions of later 
date have the same primary origin as these in the Pine Lake granite 
is a question worthy of investigation ; but the study of this occurrence 
shows that “ contemporaneous veins ” of an acid character may be formed 
not only during the final stage of crystallization, as in the case of the 
hysterogenetic schlieren and the “ kluftblitter” of Reyer, but that highly 
silicious portions are sometimes segregated or differentiated out of a gran- 
ite magma before crystallization, and that the banded structure often 
seen in pegmatites and other allied bodies and sometimes cited as proof 
of their aqueous deposition in preexisting fissures is not necessarily so 
produced, but, as is now being generally recognized, may and usually does 
result from the primary crystallization of the cooling magma. 
