er during submergence, they might be connected with the
quartz veins of the Piedmont plain. That theory, however, with
difficulty accounts for their well-rounded condition, which shows
either beach action or long carriage. The quartz sand may well have
been derived from the granitic quartzes, but that is an uncertain
matter. The sandstones and quartzites are usually massive and pure
white, of the variety found along Catoctin and Bull Run mountains.
Other varieties of sandstone--the blue-banded type, for instance--are
derived from the Weverton sandstone on the Blue Ridge. The white
sandstone pebbles in the terraces along Bull Run Mountain can be
traced from the ledges to the deposits. In this region, therefore, an
absolute shore can be seen. In other areas along Catoctin Mountain a
shore can be inferred, because the mountain projects above the
baselevel plane and contains no gravel deposits. In fact, only a few
points at the stream gaps are cut down to the baselevel.

_Metamorphism._

Dynamic metamorphism has produced great rearrangement of the minerals
along the eastern side of the Catoctin Belt, and results at times in
complete obliteration of the characters of the granite. The first step
in the change was the cracking of the quartz and feldspar crystals and
development of muscovite and chlorite in the cracks. This was
accompanied by a growth of muscovite and quartz in the unbroken
feldspar. The aspect of the rock at this stage is that of a gneiss
with rather indefinite banding. Further action reduced the rock to a
collection of angular and rounded fragments of granite, quartz, and
feldspar in a matrix of quartz and mica, the mica lapping around the
fragments and rudely parallel to their surfaces. The last stage was
complete pulverization of the fragments and elongation into lenses,
the feldspathic material entirely recomposing into muscovite,
chlorite, and quartz, and the whole mass receiving a strong
schistosity, due to the arrangement of the mica plates parallel to the
elongation. This final stage is macroscopically nothing more than a
siliceous slate or schist, and is barely distinguishable from the end
products of similar metamorphism in the more feldspathic schists and
the Loudoun sandy slates. The different steps can readily be traced,
however, both in the hand specimen and under the microscope.

The Weverton sandstone has suffered less from metamorphism than any of
the sediments. In the Blue Ridge it has u