120 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
porphyry. The passage of felsite into syenite has been noted in 
Canada by Bailey (’79, p. 3 DD). 
The transitions bear a strong resemblance to those shown in the 
stages of zones 7 and 6 (i. e. the hornblendic granite and the 
biotitic granite porphyry) from the classic locality at Willey Notch 
in the White Mountains (Hawes, ’81), where the granite became a 
quartz porphyry, with the same conspicuously weathering feldspars 
in a dark ground mass, near the contact. 
While there is no evidence of a line of contact between the gran¬ 
ite and quartz porphyry type, we do hnd near the quarries on Pine 
Hill, and also near the summit of Wampatuck Hill, an irregular line 
of abrupt demarcation between the porphyritic and the lluidal apo- 
rhyolite; the same being traceable for a long distance. This appar¬ 
ently indicates that the latter was a flow at subsequent time, especially 
as the general weathering of the fluidal lines follows a direction in 
general parallel to the contact. The distinction, however, is no 
more marked than has been known to occur in New Brunswick and 
elsewhere in superficial portions of the same flow. In the building 
up of the batholite from a magma of undifferentiated composition 
that portion of the molten magma which failed to reach the surface 
naturally cooled very slowly, giving an opportunity for all its com¬ 
ponent minerals to crystallize out separately; but as various crystals 
interfered with each other’s growth, only those first formed could 
approximately attain their normal crystalline outlines. Therefore 
a holocrystalline or granitic texture was the result (PI. 1, Figs. 2 
and 3). The outer portion of the magma, which was thrust to the 
surface before more than a few of its components had had time to 
crystallize, became suddenly chilled, giving rise to the porphyritic 
type of rocks (PI. 1, Fig. 4), which would in composition most 
nearly represent the original proportion of the constituents in the 
undifferentiated magma, and which, as proved by chemical analysis, 
would therefore occupy the position of a mean in composition, 
between the more highly differentiated extremes of the granite and 
the (devitrified) fluidal rhyolites. The remaining mineralizers of 
the surface crust in part formed a ground mass like the granite 
texture on a small scale, termed a micro-granitic ground mass, or 
else formed an amorphous glass which in these old rocks has under¬ 
gone a subsequent change through the process of devitrification. 
For these devitrified rhyolites Dr. Bascom proposes the term apo- 
rhyolite , employed in this paper. The devitrification process casued 
