e point they have been worked for commercial
purposes. Nearly every outcrop has been opened, however, for
agricultural lime. Where Goose Creek crosses this belt a quarry has
been opened and good marble taken out, but want of transportation
facilities has prevented any considerable development. The relation
between marble and schist is very perfectly shown at an old quarry
west of Leesburg. The marble occupies two beds in schist, and between
the two rocks there is gradation of composition. In none of the
western belts are the calcareous beds recrystallized into marbles,
but all retain their original character of blue and dove-colored
limestone. None of them, however, is of great thickness and none of
great linear extent.

The Loudoun formation, of course, followed a period of erosion of the
Catoctin Belt, since it is the first subaqueous deposit. It is
especially developed with respect to thickness and coarseness to the
west of Catoctin Mountain. Elsewhere the outcrops are almost entirely
black slate. This is true along the Blue Ridge, through almost its
entire length, and also through the entire length of the Catoctin
Mountain. On the latter range it is doubtful if this formation exceeds
200 feet in thickness at any point. Along the Blue Ridge it may, and
probably does, in places, reach 500 feet in thickness.

The distribution of the coarse varieties coincides closely with the
areas of greatest thickness and also with the synclines in which no
Weverton sandstone appears. The conglomerates of the Loudoun formation
are composed of epidotic schist, andesite, quartz, granite, epidote,
and jasper pebbles embedded in a matrix of black slate and are very
limited in extent.

_Weverton Sandstone._

The formation next succeeding the Loudoun formation is the Weverton
sandstone. It is so named on account of its prominent outcrops in
South Mountain, near Weverton, Maryland, and consists entirely of
siliceous fragments, mainly quartz and feldspar. Its texture varies
from a very fine, pure sandstone to a moderately coarse conglomerate,
but, in general, it is a sandstone. As a whole, its color is white and
varies but little; the coarse beds have a grayish color in most
places. Frequent bands and streaks of bluish black and black are added
to the white sandstones, especially along the southern portion of the
Blue Ridge. The appearance of the rock is not modified by the amount
of feldspar which it contains.

From the distributio