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ANDROSCOGGIN COUNTY.
47
reservoir
was under construction at the time of the writer's visit, and many
exposures then showing have since been covered. The schists, which in
general are purplish gray in color, have been intensely injected by
pegmatite, though the largest pegmatite lens observed was 10 feet long
and 2-1/2 feet in greatest width. The injection does not in all
places take the form of definite lenses or stringers of pegmatite, but
in many the impregnation of the'schist is so intimate as to obscure
almost entirely the schistose structure and develop a speckled
appearance. The sedimentary origin of the schist is shown by tlie
general evenness and regularity of its trend and by the local
preservation of bedding in its more quartzose layers.
Danville Corners.- An
exposure of considerable interest was observed in a road cut about
half a mile southeast of Danville Corners, where the rock, which has
been recently blasted, is for the most part a gray granite, of slightly
gneissic texture. It is phanerocrys-talline, most of its mineral grains
ranging from 1 to 2 millimeters in diameter and its texture is
typically granitic. The faint gneissic texture is due to a parallel
orientation of many of the biotite plates, to their slightly greater
abundance along some planes than along others, and to slight
differences in the coarseness of certain bands as compared with others.
Under the microscope the constituents are seen to be quartz, orthoclase
and microcline, albite, biotite (altering to chlorite), and some
muscovite. their relative abundance appearing from casual examination
to be in the order given.
This
granite gneiss is associated with subordinate amounts of pegmatite,
which is not so coarse as much pegmatite found elsewhere, but is
typically pegmatitic in texture. The pegmatite specimen collected for
detailed study shows feldspar crystals up to one-half inch across and
aggregates of feldspar crystals unmixed with other constituents 1 inch
across and areas of smoky quartz one-half inch across. Muscovite
crystals are one-eighth inch across and biotite crystals one-fourth
inch. Garnets up to one-sixteenth inch in diameter occur. Texturally
the pegmatite differs from the granite gneiss in showing a much greater
range in size in the mineral grains of each species and much less
evenness in their distribution. In the pegmatite there is a marked
tendency toward segregation of the different mineral constituents,
some areas being dominant!}' feldspar and others dominant^ quartz.
This feature is entirely distinct from mere increased coarseness of
grain.
The
constituents of the pegmatite are identical with those of the granite
gneiss, being (1) quartz, (2) orthoclase and microcline,
(3)oligo-clase-albite with some border rims of albite, (4) biotite, and
(5) muscovite, the numbers showing the order of their apparent
abundance. The principal difference in their mineral composition is the
much smaller quantity of biotite present in the pegmatite. Inclusions
are abundant
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