1880.] NATURAL SCIENCES OF PHILADELPHIA. 267 



Philadelphia ; (2) that at a higher elcA'ation there are deposits of 

 superficial yellow brick-cla}' quite distinct from the underlying 

 plastic clays ; (8) that boulders identical with those on this side 

 of the river occur in the brick-clay ; (4) that a stratified red gravel 

 containing Triassic shale, and similar to the University gravel 

 occurs ; and, (5) that there are indications of the existence of a 

 Terrace, several miles from the river, bounding the brick-clay and 

 its boulders, and composed of an older, and probably oceanic, 

 gravel and sand. 



The Fossiliferoiis Gravel. — There seems to be evidence that 

 between the Upland Terrace and the River Gravel Terrace there 

 is an intermediate terrace, back of which is a gravel somewhat 

 different from the Philadeli)hia red gravel. It is characterized by 

 comparative absence of Triassic red shale, and by the presence of 

 numerous pebbles of flint, hornstone, or limestone, which are fre- 

 quently fossiliferous. These pebbles, as well as those of white 

 quartz, are not fresh-looking, but are eaten and weather-worn by 

 age. In both its position and its appearance it is an older forma- 

 tion than the red gravel. It is of a 3'ellowish color, becoming- 

 white when exposed to the weather, and is more sandy than the 

 red gravel. For these reasons it is less esteemed for road-making. 

 The Germantown Railroad cuts through this gravel at New York 

 Junction, We have found here pebbles containing Cyathophyl- 

 loid corals, Favosites, a Trilobite, etc. The Connecting Railroad 

 at Ridge Avenue Station cuts through the same gravel, and here 

 we have found Strophomena^ etc. Other fossils have been found 

 below the ela}' in the East Park and at the Centennial Grounds. 



This gravel is found on the high level plateau which lies at the 

 base of the Upland Terrace, and is covered b}^ more recent brick- 

 cla3^ It lies farther from the river and at a higher elevation than 

 the red gravel, and there is a decided rise in the ground from the 

 latter to the former. This terrace has been observed in many 

 places near and in the city, but has not as yet been traced con- 

 tinuously, and its existence is doubtful. Nearly- all the brick-3'ards 

 in tlie city, exceijt those in the " Neck," lie upon this gravel and 

 back of this terrace, which lies at a mean distance of about a mile 

 inside of the Upland Terrace. It seems as though the flood, 

 diminishing in breadth, had eroded away the clay within this •' Red 

 Gravel Terrace." The red gravel comes to the surface, with 

 very little overlying cla}', at elevations below about 100 feet; 

 while at a higher elevation is the brick-yard plateau. 



