1880.] NATURAL SCIENCES OF PHILADELPinA. 259 



Railroad, which run parallel with the Delaware River, do not 

 rise out of the region of drift. 



Now, connecting by a line the four points mentioned, it will 

 be found to represent a long straight hill 200 feet or more in 

 height, having a northeast and southwest trend, pai'allel to the 

 river, and lying at a mean distance from it of about four miles. 

 We have traced it from Bucks County, thi'ough Philadelphia and 

 Delaware Counties, into the State of Delaware, and find that it 

 uniformly defines the western boundarj^ of the drift. This hill is 

 easily recognized where uncrossed by creeks, being remarkably 

 straight and of uniform height. It forms the limit of tidewater, 

 and is recognized where it crosses streams by the occurrence of 

 rapids or falls. Being the first hill of importance west of the 

 Delaware, it often commands a fine view and is a favorite site for 

 residences. The geographical position of this ancient terrace 

 may be more exactly defined in the vicinity of Philadelphia, as 

 the hill which crosses Second Street Pike near Foxchase, and 

 crossing Tacony Creek farther south, runs nearly parallel with 

 it as far as Crescentville ; which crosses Green Lane and New 

 Second Street road near the place of Mr. J. L. Fisher ; crosses the 

 North Pennsylvania Railroad above Olney road, and the York 

 road below the Jewish Hospital ; which crosses Germantown 

 Avenue at the railroad bridge (being here called Negley's Hill), 

 and running along the railroad to beyond Wayne Station, passes 

 back of the Germantown Cricket Ground, past Old Oaks Cemetery 

 to Falls of Schuylkill. Thence, passing Chamouni, Belmont, and 

 Geoi-ge's Hill, it crosses the Pennsjdvania Railroad near Heston- 

 ville, and Haverford Road at Haddington ; passes back of the 

 Burd Orphan Asjdum into Delaware County, and runs north of 

 Kelleyville, Clifton and Morton to Swarthmore College, and 

 thence past Village Green into Delaware. 



This hill, which is approximately parallel not only to the river, 

 but also to the shore of the Atlantic Ocean and to the line of 

 strike of the Cretaceous formations of New Jerse}^ forms, as we 

 have seen, the main dividing line between the ancient and the 

 modern formations. 



We shall call it for convenience the Upland Terrace. The strike 

 of the gneiss forming it corresponds closely with the trend of the 

 terrace itself. A boulder-bearing clay rests upon its southeastern 

 slope at a uniform elevation of 150-170 feet above mean ocean- 

 level. While it is true that, as will appear hereafter, there are 



