this
picture is quite quartzose, with masses of pure quartz 4 to 5 feet
across. The feldspar is in small crystals intergrown with quartz and
mica and does not occur in large crystals comparable to the quartz
masses. The quartz stringers of the schist are traceable in many
instances with perfect continuity into the quartz of the schist, and a
number of the quartz stringers contain muscovite crystals. Within 11
feet of the main pegmatite mass the schist becomes darker colored
through the abundant development in it of dark-brown tourmaline.
On
the east shore of Kennebec Point, about half a mile northeast of the
extreme southern tip, schists are intruded by pegmatitic granite
similar in mineral composition to the coarse pegmatite at the Golding
quarry, its principal constituents being quartz, potash feldspar,
muscovite, and black tourmaline. The average size of grain in this
granite is not over one-fourth inch, although some of the feldspars
are 3 inches long. None of the black tourmaline crystals are over
one-fourth inch and they average only about one-eighth inch in width.
It is significant that the minerals, especially the black tourmaline,
show a noticeable amount of parallel orientation in certain parts of
the ledge, indicating a certain amount of flowing movement during
crystallization. The rock becomes finer grained within 8 or 10 inches
of the schist contact. This rock gives every indication of being
intermediate in its character between normal granite and the typical
coarse pegmatite of this region.
TOPSHAM.
The
rocks of the town of Topsham are quartz-mica schists which have been
intruded by pegmatite, by flow gneisses of granitic composition, and
to some extent by granite. Exposures showing the characters and
relationships of these rocks are plentiful and excellent.
Distribution of the quarries.—The
pegmatites of the town are now worked for feldspar at several points
and were once worked at a number of others now abandoned. The quarries
all lie within a belt about a mile in width, extending from Mount
Ararat, near Topsham village, in a northeasterly direction nearly to
the Topsham-Bowdoin-ham line. Within this belt are eight quarries, only
three of which are now active, and a number of prospect pits. It is
significant that the line of distribution of these quarries corresponds
closely with the trend of the metamorphosed sedimentary schists into
which the pegmatites were intruded. Because of the soil covering it is
impossible to determine the exact limits of the coarse pegmatite
bodies exposed at each of these eight quarries, but it is evident from
a study of the rocks between the various quarries that the pegmatite
bodies which are worked are not all of them parts of a single pegmatite
mass but are more or less detached intrusions in a region where the
