2T0 PROCEEDINGS OF THE ACADEMY OP [1880. 



Home, near which place have been found a sharp boulder of conglom- 

 erate three feet in diameter, several fragments of ferruginous sand- 

 stone equally large, a partially rounded boulder of white quartz 

 nearly four feet long, and numerous fragments of quartzite and 

 Primal rocks. The gravel is here in part replaced by clay. 



A similar tract of this gravel occurs at Bryn Mawr, extending 

 from that place to near Cooperstown. A good section is exposed 

 in the railroad cut below the station. From this locality, so easy 

 of access from the city, we have named the formation. It is 

 here about 430 feet high, and nine miles from the river. The 

 gravel is ten feet deep, and lies upon a steepl^'-dipping gneiss so 

 completely decomposed that it is as soft as cla3^ Underneath the 

 bridge, a soft Avhite kaolin-like material, conformable with the 

 gneiss, shows a decomposed steatite,^-being probably the con- 

 tinuation of that which crosses the Scimylkill at Laftiyette. Here, 

 as at Chestnut Hill, the gravel lies in an isolated patch upon a hill, 

 distant from any stream or other eroding agency. The gravel 

 holds sharp fragments of primal rocks and also the iron con- 

 glomerate. As at Germantown, the fields below, to the south, 

 contain occasional fragments of the conglomerate. 



Another good exposure of the Bryn Mawr gravel is on a hill 

 crossed by the road leading from Haverford College to Coopers- 

 town. The conglomerate is here in large, sharp fragments, and 

 the gravel shows slight horizontal sti'atification. On the crest of 

 the hill, some 450 feet high, there is a weather-worn boulder, 

 four feet in diameter, of a soft, coarse, brown sandstone of Br^'n 

 Mawr age, apparently in place. 



A fourth, precisely similar exposure of gravel Avith conglom- 

 erate, and at about the s:ime elevation, caps the hill back of Media, 

 near the lloseti'ee. 



Without describing any further exposures, it already appears 

 that in these elevated patches of ancient gravel we have the last 

 remnants of a once continuous formation. The very great erosion 

 which has swept away all but these few traces is a sufficient proof 

 of its age. There are no points at all approaching the elevation 

 of these hills, between them and the Atlantic Ocean ; and it is at 

 once suggested that these patches are the remnants of an oceanic 

 deposit, possibly of Tertiary age. It is interesting to find that a 

 precisely similar formation caps some of the hills in New Jersey. 

 On top of the hill at Mount Holl}^, N. J., is an identical con- 



