MARYLAND GEOLOGICAL SURVEY 101

were contributed to Plate IV in " Correlation Papers, the Newark
System, " by I. C. Russell. ¹

In the summer of 1891 there was issued by the survey a preliminary
edition of the Washington sheet, with the geology of the crystalline
rocks by Dr. Geo. H. Williams, and of the overlapping sedimentary
rocks by N. H. Darton. There was also prepared by Dr. Williams
and Mr. Darton, jointly with Messrs. W J McGee and B. Willis, an
account of the geology of Washington and vicinity for the " Guide to
Washington and its Scientific Institutions, " printed for the Fifth Ses-
sion of the International Congress of Geologists.

During 1891-92 Dr. Williams continued field work in the area of
crystalline rocks in Maryland. Work in the Baltimore quadrangle
was completed, and in February, 1892, there was published for the
American Institute of Mining Engineers a guide-book to Baltimore
containing a description of the geology of that region, the crystalline
rocks by Dr. Williams, and the sedimentary rocks by Mr. Darton,
accompanied by the preliminary map, " The Baltimore Sheet, " pub-
lished by the United States Geological Survey. This map, with
somewhat extended area, was republished by Johns Hopkins Univer-
sity as a " Geological Map of Baltimore and Vicinity, " by G. H.
Williams and N. H. Darton.

In 1892-93 Dr. Williams's studies were mainly directed toward
mapping portions of the Ellicott and Laurel quadrangles, the deter-
mination of the rocks in Cecil county, an examination of the eruptive
rocks in the South Mountain region, and a re-examination of crystal-
line rocks in the West Washington quadrangle, with a view to the
publication of the final Washington folio.

In 1893-94 the time and survey allotment at Dr. Williams's
disposal were limited, but considerable progress was made in mapping
the crystalline rocks of the Gunpowder, Laurel and West Washington
quadrangles. He also prepared a preface on " The general relations of
the Granitic Rocks in the Middle Atlantic Piedmont Plateau " for the
report by Mr. C. R. Keyes on " The Origin and Relations of Central
Maryland Granites. "² His last field work for the survey was in the

¹ Bull. U. S. Geol. Survey No. 85, 1892.

² Fifteenth Ann. Rept. U. S. Geol. Survey, 1895, pp. 651-740, pls. 27-48.