best adapted for study, because it is connected directly with the
usual time scale by its associated deposits. This stage is the
Tertiary baselevel, and the deposit is the Lafayette formation, a
deposit of coarse gravel and sand lying horizontally upon the edges of
the hard rocks. Over the Coastal plain and the eastern part of the
Piedmont plain it is conspicuously developed, and composes a large
proportion of their surfaces. As the formation is followed westward it
is more and more dissected by erosion and finally removed. Near the
area of the Catoctin Belt it occurs in several places, all of them
being small in area. One is three miles northeast of Aldie. Here, a
Newark sandstone hill is capped with gravel. This gravel is much
disturbed by recent erosion and consists rather of scattered fragments
than of a bedded deposit.

The materials of the Lafayette gravel are chiefly pebbles and grains
of quartz, with a considerable admixture of quartzite and sandstone.
The large quartz pebbles were probably derived from the large lenses
of quartz in the Catoctin schist, for no other formation above water
at the time contained quartz in large enough masses to furnish such
pebbles. On the hypothesis that they were of local origin and merely
worked over 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