Mineral Industries and Geology of Certain Areas - Vermont Agency ...

REPORT OF THE VERMONT STATE GEOLOGIST. 51
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caught tip by the granite, which is marked on the map by shading
in the southeastern part of the township. These masses of
the schist now appear as inclusions in the walls of the granite
quarries. They are of all sizes from a few inches to thirty feet
or more in length. One of the larger included masses is represented
in Plate VII. It will be seen by an inspection of
the map that a limb of the schist passes almost across Millstone
Hill, as if to make two portions of the granite at that
point. The outcrop of schist does not continue uninterruptedly
over the area represented for that rock, from north to south,
although the ledges are continuous over much of it. No granite,'
however, is found between them, until one comes to the
southern border of the hill. Other lesser hands of the country
rock, which are too small to be represented on the map, extend
into the granite in the same way. It is evident, therefore, that
at the time of iltrusiofl of the igneous rock large portions of
the schist were carried away, while others were left extending
into the granite as broken bars.
The contact effects are everywhere slight. Usually a darkened
rim, scarcely over a centimeter in width, marks the indurated
metamorphic rock where it stands against the granite.
No new minerals are developed, but biotite is here more abtindant
than througilout the renlainder of the schist. In Plate
VIII such a contact zone may be seen, extending between the
granite on the right hand and the schist on the left.
Description and Petrography of the Granite Area.—Over much
of the granite area the drift cover is heavy. The rock obtained
on Cobble Hill, a mile and a half to the north of Millstone Hill,
is of an inferior grade. Nearly all the more interesting expostires
lie in the soutilern half of the granite area, as represented
on the map, and this southern portion yields more than ninetenths
of all the granite producecl by Barre township. All the
inlportant quarries are located on the eastern or southern slopes
of Millstone Hill, or inlmedliately to the south of it. Where
the joints are irregular and crowded together "boulder quar-