AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[THIRD SERIES.] 
ArT, XXXIV.—On the Surface Geology of Southwest Pennsyl- 
vania, and adjoining portions of Maryland and West Virginia ; 
by Joun J. Srevenson, Professor of Geology in the Uni- 
versity of New York. 
THE following article contains a brief summary of the re- 
sults obtained by me during three years’ labor in connection 
with the Second Geological Survey of Pennsylvania. The de- 
tailed statement will appear elsewhere. 
e area in which observations were made covers in all 
more than 10,000 square miles. It embraces that portion of 
Pennsylvania lying south from the Ohio and Conemaugh Rivers 
and west from the Alleghanies; includes a large part of West 
Virginia and Maryland lying on both sides of the Alleghanies 
of Virginia; and has the channel-ways of four great rivers, the 
Monongahela, Cheat, Youghiogheny and Potomac, lying partly 
t 
oF 
within it. 
main streams, : 
A second series of benches appears throughout this whole 
region and seems to be characteristic of a much wider area 
than that in which observations were made. The benches of 
this series evidently differ in origin from those of the lower se- 
nes ; their detrital coating contains little clay, no transpo 
fragments and consists almost wholly of sand. They are almost 
absolutely horizontal ; they do not merge into the lower series, 
Am. Jour. Sct.—Tutrp Sertzs, Vou. XV, No. 88.—APRIL, 1878. 
17 
