1880."] NATURAL SCIENCES OF PHILADELPHIA. 299 



that this formation has a depth on Delaware Avenue, Philadelphia, 

 of about 50 feet, and that it extends up to about Third and Market 

 Streets. On Smith's Island and on the bar in the river opposite 

 Cooper's Point, it is 100 feet deep, lying upon rock. It therefore 

 underlies the river, filling up its ancient channel. On Richmond 

 Street some verj- large boulders are seen lying upon the sand. 



On tracing the Trenton gravel up the river, it is found to be 

 confined to its immediate vicinity, and that, from Philadelphia to 

 the Neshaminy Creek, its boundary is generally between the linO: 

 of the Pennsylvania Railroad and the Delaware. From this point 

 the bounding terrace trends directlv towards MorrisviUe and 

 away from the present river. Thus, at Bristol, the gravel and its 

 overlying sand extends two miles back from the river, and is. 

 bounded b^' a well-marked hill, upon which lie the older gravel 

 and brick-clay of Champlain age. These and the Tertiary gravels, 

 extend nearl}' seven miles inland. At Tullytown the Trenton 

 gravel extends two and a-half miles back, and at the canal shows 

 the following succession of strata : (1) sandy loam, 1 foot ; (2) fine 

 gray "moulding-sand," 2| feet; (3) shai-p "bar sand," 1 foot; (i) 

 clean gray river gravel of unknown depth. In other openings 

 near here the gravel is so full of boulders that these are dug in 

 large quantities and sent to Philadelphia for " cobble-stones." 

 Near Wheatsheaf Station, close to the railroad,. an opening which 

 has exposed a section of the Trenton gravel nearly half a mile in 

 lenoth. exhibits well the general features of the formation. The 

 pebbles, of characteristic shape and color, are made of gray Triassie 

 argillite, slate, red shale, sandstone, conglomerate, and various:, 

 other rocks found farther up the valley, while large and often 

 sharp boulders of red shale and other materials frequently occur. 

 The whole formation has a A-ery fresh appearance when compared 

 with older gravels. Xear Turkey Hill a large smooth boulder, 

 five feet in diameter, lies upon the sand. 



At MorrisviUe the narrower portion of the valley begins, and 

 from here up, the river flows on arockA* bottom, and the gravel is 

 shallow and is confined to the immediate vicinity of the river. 

 The older gravels of oceanic origin continue across New Jersey 

 and do not appear above Yardleyville. The Philadelphia red 

 gravel is no more seen, but the brick claj' with its boulders occa- 

 sionally appears part way up the steep hills enclosing the valley,, 

 and is abundant in the side valleys formed by tributary streams. 



