MARYLAND GEOLOGICAL SURVEY 99

mapped by Mr. A. E. Murlin. In the following years those in the
mountains were revised for the purpose of adapting them to the two-
mile scale, and in 1895 and 1896 those on the eastern shore were
mapped, thus completing the mapped area of the state. This is shown
on the small accompanying map. The tier of partial quadrangles just
south of the Pennsylvania line, in the western part of the state, was
originally surveyed for publication on the four-mile scale, and this
area has never been revised to adapt it to a larger scale.

GEOLOGIC WORK.

The earliest geologic work carried on by the United States Geo-
logical Survey in Maryland was, as has been said, of the nature of
reconnaissance, with chief reference to the general stratigraphic rela-
tions. There followed from time to time the detailed mapping of
certain formations, accompanied by extensive laboratory study of
crystalline rocks, and field and laboratory studies of fossil plants and
animals. The work is conveniently described under three geographic
heads, the Piedmont Plateau, the Appalachian Region, and the Coastal
Plain.

Piedmont Plateau.

The principal work of the Survey in the Piedmont region was
conducted by Professor George H. Williams, of the Johns Hopkins
University, who for several years made detailed studies of the crystal-
line rocks and their relations under the joint auspices of the Geological
Survey and the University.

His field work for the Survey began in the spring of 1888, but
for several years prior to this he had been engaged in the study of the
crystalline rocks in the vicinity of Baltimore, some of the results of
which were published in a government bulletin entitled " The Gab-
bros and Associated Hornblende Rocks occurring in the neighborhood
of Baltimore, Maryland. " ¹

His principal work in 1888-89 was carried on along two distinct
lines and with two distinct sets of problems in view. First, to trace
out the relations of the slightly crystalline or non-crystalline rocks

¹ Bull. U. S. Geol. Survey No. 28, vol. iv, 1886, pp. 613-688.