into
which they are intruded are in some places granites, but are generally
foliates," either schist or gneiss. The foliates are in many places
dynamically metamorphosed sediments, but in others are unquestionably
primary.
PEGMATITES IN FOLIATED ROCKS.
General statement.—Though
showing minor irregularities of form, most of the pegmatite masses in
the foliated rocks are of sheetlike character and lie parallel or
nearly parallel to the schist or gneiss folia. If the foliates are
steeply inclined the pegmatite exhibits a dike like form (PI. Ill, A) if they are flat-lying the pegmatite mass assumes a sill-like form (PI. Ill, B).
Another
feature highly characteristic of pegmatite masses in foliates is their
tendency to swell and thin along their trend so as to form virtually a
series of connected lenticles. (See fig. 1.)
The
contact between pegmatite and foliate is in nearly all areas very
sharp, whether the pegmatite lies parallel to or cuts across the folia
and whether its mass is large or small. In many places (see PI. IV, A, B) the pegmatitic intrusion is so intimate that the bordering schist becomes an injection gneiss. Such gneisses
