392 ORGANIC REMAINS IN AND AROUND PHILADELPHIA. 



Maclure, the best authority extant, informs the public, 

 in the new edition of the Geology of the United States of 

 America, &c. just published by Abraham Small, (p. 33), 

 that the " city of Philadelphia stands upon primitive rock, 

 though, at the Centre-Square, thirty or forty feet of sand 

 and gravel must be penetrated before the gneiss rock, 

 which ascertains the formation, is found." 



Dr. Amos Gregg has stated that the land where Bristol 

 stands, is made ground, and that within no great period 

 of time. As a confirmation of the opinion, about twenty- 

 five feet below the surface, the earth is found to be the 

 same with that of the adjacent marsh, to wit, a black 

 mud. Both are nearly upon a level. At that depth, in 

 several places, have been found large sticks or rather 

 logs of wood, sound and uninjured by the waste of time, 

 except about a quarter of an inch on the surface. He 

 thought they were of pine. 



At this place the geological appearances are so pecu- 

 liar, that Mr. William Bartram was led to conclude, the 

 low marsh, meadows, and ponds, situated N. W. of the 

 borough, were once the bed or channel of the Delaware, 

 and that the present bed of that river was a low isthmus 

 which connected it with the firm land of New-Jersey. 



The following extract from the Picture of Philadelphia. 

 published by James Mease, M. D. shows the topographi- 

 cal character of the bottom upon which the city stands, 

 (p. 15, 16.) The " immediate substratum of Philadel- 

 phia is a clay of various hues and degrees of tenacity 

 mixed with more or less sand, or sand and gravel. Un- 

 derneath, at various depths, from twenty to nearly forty 

 feet, and also on the opposite shore of New-Jersey, are 

 found a variety of vegetable Remains, which evidently 



