50 The American Geologist. January, i897 
THE RELATION OF THE STREAMS IN THE NEIGH- 
BORHOOD OF PHILADELPHIA TO THE BRYN 
MAWR GRAVEL. 
By F. Bascom, Bryn Mawv, Penn. 
In a paper upon "The Rocks near Philadelphia,"* which 
was published in the Proceedings of the Academy of Natural 
Sciences of Philadelphia, occurs the following statement: 
"A remarkable feature of the part of Montgomer}'^ county 
and Chester county bordering on the Schuylkill is the direc- 
tion taken by the streams. The general features are high hills 
extending in a northeast and southwest direction, with deep 
limestone valleys between, nearly at right angles to the gen- 
eral course of the Schuylkill. 
"The streams, however, do not follow the valleys. The Wis- 
sahickon leaves the Montgomery county valley and flows 
eastwardly through a deep, narrow gorge, through very hard 
rocks, a distance of over five miles. The Valley creek flows 
down the Chester valley and then turns abruptly westwardly, 
and flows through the northwest boundarj^ line. The Gulf 
creek flows down the valley two or three miles, then turns 
westwardly and flows through a deep and narrow gorge into 
another valley on the west, with banks rising abruptly two or 
three hundred feet." 
These three streams, the Wissahickon, Valley creek and 
Gulf creek, whose peculiar courses are thus pointed out, are 
only the more marked illustrations of features which charac- 
terize all sti-eams of the same class, flowing over the Piedmont 
plateau, in the neighborhood of Philadelphia. 
The history of these streams will explain not only the direc- 
tions pursued by them but also by the neighboring streams. 
Were it possible to read their story completely much light 
would be shed upon the still obscure post-Newark history of 
this portion of the Piedmont plateau. 
While the following conside.-ation of the stream histor}^ is 
manifestly incomplete, it still maj^ suggest a possible criterion 
of the age of the superficial deposits of the plateau, which has 
not received much attention. 
The present topography will be more readily understood if 
the discussion of the streams is preceeded by a brief resume 
*Rand, T. D., on The Rocks near Philadelphia. Proc. Academy of 
Natural Sciences of Philadelphia, May 29th, 1876, pp. 1-4. 
