148 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165. 
stand out against the groundmass with distinct outline; but some of 
the feldspars must have continued to form and develop later than, or 
simultaneously with, the quartz. The micrographic intergrowth indi- 
cates an enforced hastening of the cooling process. All these observa- 
tions are in keeping with the idea that this is a small intruded mass 
whose present surface is probably not far from the original periphery. 
The presence of microcline, the numerous shattered grains of quartz, 
and the few broken feldspars all point to pressure on the mass after 
cooling. 
Dark aggregates in the Mapleton granite. — These either take the form 
of a mass of mica shreds and plates, in which the quartz and feldspar 
is scarcely visible, or they appear as a thick sprinkling of hornblende, 
biotite, and titanite in an area of fine-grained, light-colored rock. 
They are a foot and less in diameter and are very irregular in outline. 
An examination of thin sections under the microscope reveals an 
abundance of apatite columns, and especially needles. Some are as long 
as the mica laths and run through two or more minerals without a 
break. The titanite grains are eaten into and at times inclose other 
minerals. Biotite is strongly pleochroic and sometimes entwined with 
the hornblende. The hornblende is the brown-green variety, pleochroic, 
with good basal and prism sections, often grouped in masses and inter- 
grown with or idiomorphic against the biotite. Some sections are 
bent. The feldspar, in small laths and irregular pieces, occupies bays 
in the hornblende, biotite, and titanite, or may even be idiomorphic 
against them. What little quartz is present shows a rolling extinction. 
It is instructive to note the similarity in composition between these 
dark aggregates and the kersantite dikes described below. It is as if a 
differentiation begun in the mass had reach reached completion in the 
associated dikes. 
DREWS LAKE GRANITE. 
The granite from the Ludlow quarry is considered typical for the 
Drews Lake district. It exhibits two well-marked varieties in different 
parts of the quarry. The highest rock exposed by the workmen has a 
grayish-white color in the hand specimen and its surface is sprinkled 
inconspicuously with dark specks. Quartz shows prominent^ and 
often forms aggregates of considerable size. In the bottom of the 
quarry the granite becomes a dark-gray variety in which the dark 
components assume a leading role and quartz is scarcely noticeable in 
microscopic examination. Transitions occur between these two types. 
While the rock differs thus widely in the relative distribution of min- 
eral constituents, it retains a medium-grained, uniform texture, and 
the specimens at hand show no porphyritic tendency. 
Under the microscope the granite from Ludlow differs from that 
from Mapleton in having the iron ore often in bundles of rods within 
the biotite, in the absence of titanite, and in the presence of a little 
