surveyor's compass, rendering surveying extremely difficult where
great accuracy is required. In some instances the needle has been
drawn as much as seven degrees from its true course. This effect is
more or less observable nearly throughout the Catoctin Mountain, and
has been noted elsewhere in the County.

Chromate of iron was long ago discovered along Broad Run, and, about
the same time, a bed of micaceous iron ore on Goose Creek below the
Leesburg turnpike. Copper ore is associated with the last-named
mineral.

In 1860, the output of pig iron in Loudoun was 2,250 tons, and its
value $58,000. Rockbridge was the only Virginia County to exceed these
figures.

In several localities small angular lumps of a yellowish substance,
supposed to contain sulphur, have been found, embedded in rocks. When
subjected to an intense heat, it gives forth a pungent sulphurous
odor.

Small quantities of silver ore are discovered from time to time; but
the leads have never been extensively worked and many of the richest
veins are still untouched.

Deposits of copper in the schists have long excited interest and led
to mining operations. The amount of ore, however, appears not to have
justified any considerable work.

Near the base of the Catoctin Mountain, where it is first approached
by Goose Creek, marble of an excellent quality is found but has been