88 HISTORICAL SKETCH

Further investigation was given to the crystalline rocks of Maryland
by Dr. Williams during 1890. An article upon " The non-feldspathic
Intrusive Rocks of Maryland and the Cause of their Alteration "¹ was
published during the year.

An important " Discovery of Fossils in the Limestone of Frederick
County, Maryland"² was made by Charles R. Keyes, a student of
the Geological Department, which aided greatly in the elucidation of
the stratigraphy of the western portion of the Piedmont belt.

A former student, Professor W. H. Hobbs of the University of
Wisconsin, presented a paper to the Wisconsin Academy of Sciences in
1890 " On some Metamorphosed Eruptives in the Crystalline Rocks
of Maryland, "³ in which the work which had been carried on under
the auspices of the University was described.

In the spring of 1891 Dr. Clark organized a scientific expedition in
co-operation with members of the United States Geological Survey
and the Maryland Agricultural College for the study of the physical
features of southern Maryland. The party comprised twenty-five
members, representing, the United States Geological Survey and other
institutions both within and without the state. An extended account
of this trip was published by the University. ⁴ About this time a
memoir by Dr. Clark upon "The Eocene of the United States"⁵
appeared among the publications of the United States Geological
Survey, in which the results of his researches upon the Eocene of
Maryland found a place.

Professor Williams continued his observations upon the crystalline
rocks of the Piedmont Plateau during 1891, accounts of which are
found in the Administrative Reports of the Director of the United
States Geological Survey. A paper read before the Geological Society
of America the previous winter upon " Petrography and Structure of
the Piedmont Plateau in Maryland, "" and one by Mr. Keyes upon "A

¹ Amer. Geol., vol. 6, 1890, pp. 35-49.

² Johns Hopkins Univ. Circ. No. 84, vol. x, 1890, p. 32.

³ Trans. Wisconsin Acad. Sci., vol. viii, pp. 156-160.

⁴ Johns Hopkins Univ. Circ. No. 89, vol. x, 1891, pp. 105-109.
⁵ Bull. U. S. Geol. Surv. No. 83, 1891, pp. 43-45, 80, 86-87.
⁶ Bull. Geol. Soc. Amer., vol. ii, 1891, pp. 301-318.