258 proceedings of the academy of [1880. 



November 25, 1818. 



the surface geology of philadelphia and vicinity. 



by henry carvill lewis. 



At intervals during the past year the writer has been devoting 

 some attention to the gravels and clays of our city, and although 

 the work as yet is only preliminary, and is still in progress, it is 

 thought that a sketch of what has been done ma}^ serve to show 

 what an interesting field is open for more thorough investigation. 

 A large number of localities have been examined and many sec- 

 tions have been made, but it is proposed at present merely to 

 summarize the facts observed. 



The Upland Terrace. — 1. A traA'eller going from the city upon 

 the Germantown Railroad will notice in the cuttings for new 

 streets between Tenth and Broad Streets, and in the railroad cut 

 at New York Junction, numerous exposures of red or yellow 

 gravel, often overlaid by clay. The brickyards in the vicinity of 

 Nicetown expose large beds of brick-clay containing occasional 

 well-rounded boulders and pebbles. The land so far has been 

 comparatively level, and no rocks have been seen. Just before 

 reaching Wayne Station, rocks rise upon both sides of the road, 

 the clay and gravel disappear, and a rolling wooded country is 

 entered. A thin covering of light micaceous soil containing no 

 pebbles or boulders covers the gneissic rocks from here to Chest- 

 nut Hill. There is a great contrast between the two regions. 



2. On the Pennsylvania Railroad it will be noticed that, soon 

 after leaving the depot, gravel covers the rocks along the Schuyl- 

 kill, and as the railroad turns back from the river, a plateau of 

 clay follows. The Centennial grounds lie upon this clay, and 

 boulders are frequent. Upon reaching Fift^^-seventh Street, op- 

 posite Belmont and George's Hill, the hill is entered by a cut, the 

 rocks come to the surface, and the drift is no more seen. 



3. Again, on the North Pennsylvania Railroad gravels first 

 appear, then, on higher ground, clay, and soon after passing Green 

 Lane Station, the rocky uplands, free from drift. 



4. So, too, on the West Chester Railroad, gravels and clays 

 cover the ground up to the base of the hill on which Swarthmore 

 College stands. 



5. On the otlier hand, the New York division of the Pennsyl- 

 vania Railroad and the Philadelphia, Wilmington and Baltimore 



