within
a space 3 or 4 feet square. The pegmatite is in sharp contact with the
gneiss, into which it sends off a tapering apophysis. The latter for a
short distance from the main pegmatite mass is true pegmatite, but
beyond this becomes rapidly more quartzose. Most of this branch vein
consists wholly of quartz.
The inferences to be drawn from the relations described may be summarized as follows:
(1) The relations shown in Plate X, A, and
the fact that the changes in trend of the schists are abrupt and due to
displacement of schist blocks en masse indicate that the pegmatite
intrusions produced no extensive softening of the schists. Such
softening, when present at all, was confined to a zone an inch or two
wide immediately adjacent to the pegmatite. (2) The bending of gneiss
folia next the pegmatite (see PI. X, A) suggests that the dike,
even before its border portions had entirely solidified, behaved
essentially as a rigid body capable of transmitting differential thrust
and not as a liquid.
The
relations shown in figure 3, the fact that feldspar, muscovite, and
black tourmaline occur in many of the quartz veins, and the fact that
these veins are in some places not sharply differentiated from the
inclosing pegmatite, indicate that at least many of the quartz veins
are to bo regarded as end crystallizations from the pegmatite magma.
MOUNT MICA.
History.—Mount
Mica, a small hill situated about 1-1/2 miles east of the village of
Paris at an elevation of approximately 900 feet, is one of the most
famous mineral localities in the United States, and is known to
mineralogists all over the world because of the size and beauty of its
tourmaline crystals.
The
discovery of its mineral wealth dates back to the year 1820,° when two
students, Elijah S. Hamlin and Ezekiel Holmes, the former a resident of
the town of Paris, becoming interested in the study of mineralogy,
spent much time in searching for minerals in the exposed ledges and the
mountains around the village. In returning from one of their
expeditions in the autumn of 1820, Hamlin's eye was caught by a gleam
of green from an object caught in the roots of a tree upturned by the
wind. The object proved to be a fragment of a transparent green crystal
lying loose upon the earth which was still attached to the roots of the
tree. This was the first colored tourmaline taken from the locality
which afterwards yielded them so prolifically, but its character was
not recognized until somewhat
a Hamlin, A. 0., The history of Mount Mica, Bangor, Me., 1895. 63096°—Bull. 445—11------6
