2C8 PROCEEDINGS OF THE ACADEMY OF [1880. 



The Pennsj'lvania Hospital for the Insane stands upon the hill 

 forming this inner gravel Terrace. Its course is somewhat parallel 

 to the main Upland Terrace, and it crosses Walnut Street near 

 Fiftieth Street, and Broad Street near the Reading Coal Road cross- 

 ing. In Prof. Rogers' Geological Map of Pennsylvania, where a 

 rough attempt is made to represent the boundary of the drift, the 

 line in one place corresponds quite closely with what we have pre- 

 sumed to be the "Red Gravel Terrace ; " but it appears that in most 

 places in that map the boundary is meant to be merely a hypoth- 

 etical one. While the existence of this inner terrace is yet doubt- 

 ful, and while it is probable that red gravel will be found above it and 

 fossiliferous gravel below it, yet nothing has yet appeared to con- 

 trovert the assumption that the latter gravel is older than the 

 former. How much older, and whether of oceanic or of fresh- 

 water origin, is not yet determined. Here, again, a study of the 

 New Jersey gravels will be of assistance. 



The Branch town Clay. — Having now described the surface 

 deposits lying between the Delaware River and the Upland Ter- 

 race, it remains to point out the existence of some isolated patches 

 of gravel and clay which have been noticed on some of the hills 

 back of and above this terrace. 



In the village of Branchtown, on a plateau 250 feet above the 

 river, there is a local deposit of brick-cla}' \yh^g in an oblong belt 

 runnhig N. E. and S. W., perhaps a mile in length and an eighth 

 of a mile in breadth. That it is not a clay formed in place by 

 decomposition of the gneiss is shown hy the presence in it of 

 pebbles and rounded boulders of foreign rocks. The smaller 

 pebbles consist of quartz, and the larger of a friable quartz sand- 

 stone, prob?.bly Potsdam. Not a single fragment of Triassic red 

 shale, and not a single pebble of flint or fossiliferous rock was 

 found: and in this it is distinguished from any deposit heretofore 

 described. Nor were an^^ of the pebbles formed of the materials 

 of the bed of the Delaware River. Numerous sharp fragments, often 

 six inches square, of white or yelloAv siliceous sandstone and of 

 brown jaspery quartzite, both probably of lower Silurian age, were 

 f'jund. The peculiar conglomerate described below as "Mt. Holly 

 Conglomerate" does not occur. Decomposed gneiss lies below 

 the cla}^., which is two to three feet deep. The presence of sharp and 

 rounded boulders of a rock in place farther north suggests an 

 overland flood during glacial times ; but the complete absence of 



