1884.] NEW YORK ACADEMY OF SCIENCES. 27 



County, where the Glacial Drift was found resting upon the 

 yellow sand and gravel, the line of demarkation being sharply 

 defined. I visited some of these localities last September with 

 Professor Cook, and was impressed with the contrast in appear- 

 ance between the two formations, the upper, glacial deposits 

 being markedly red from the abundance of red triassic sliale 

 and sandstone, here the most abundant rocks of the moraine. 

 The yellow, pre-glacial drift at these points rests dii'cctly on the 

 Cretaceous strata, being immediately in contact with a red clay 

 on the Forbes Farm near Woodbridge,* and with a white tire- 

 clay at Inness' pits, the clays underlain by a bed of feWbpar 

 in small fi'agments. 



The modified glacial drift of the lower Delaware Valley over- 

 lies the pre-glacial drift unconformably, fi'om Trenton, where 

 the contact is well exposed, to Philadelphia, where they have 

 been studied and described by Prof. H. Carvill Lewis.f From 

 his observations it appears that about Philadelphia there is quite 

 a series of quaternary deposits overlying the pre-glacial drift. 



The materials composing the pre-glacial drift are remarkably 

 constant in character. They consist of gravel varying in size 

 from pebbles somewhat larger than a hen's egg to a fine sand, 

 which in some places is slightly charged wH[th clay. The bulk 

 of the formation is, however, coarse, and frequently exhibits 

 the " flow and plunge " structure and cross bedding, indications 

 of its deposition in disturbed waters. These sands and gravels 

 are mainly of quartz ; the pebbles and grains are very generally 

 rounded, though angular fragments occur. The whole forma- 

 tion is light-colored, generally yellow, and varying to white. 

 Examination of the larger pebbles shows that the yellow 

 eoloration is superficial ; they are lighter in tint and some- 

 times white within. The hydrated oxide of ii-on, to which 

 the color is due, is discharged l)y warm hydrochloric acid. 

 These facts indicate that this coloring has obtained since their 

 deposition. The presence of numerous beds of limonite, asso- 

 ciated with the gravels and sands, gives a clue to the origin of 

 the yellow color. It would seem probable that the whole 

 formation has been saturated with iron oxide, which has locally 

 been in sufiicient amount to cement the materials into a brown 



* Ann. Rep. State Geologist, 1880, p. 90. 

 t Joum. Franklin Inst. , June, 1883. 



