Lyman.] ^^^ [May IS, 



logical structure is nearly everywhere quite clear ; only witliin a semi- 

 circle for a dozen miles north, west and south of Somerville the indications 

 are not quite certain, and more thorough field work is especially desirable 

 there. Elsewhere, too, the limits of the diSerent subdivisions cannot be 

 supposed to be very precisely marked. In the main, however, the geolog- 

 ical structure given in the map seems unquestionable and unmistakablj'^ 

 confirmed by the published dips, by the topography, by the trap sheets 

 and by the perfect correspondence and harmony throughout of one part 

 with another. 



It is readily seen from the map and its sections that the fossil horizons 

 of Weehawken and Shadyside belong to the lower part of the Norristown 

 shales, and the horizon of Newark and Belleville to the upper part of 

 the same, as indicated also by the close lithological resemblance of the 

 brown building stone of tliese places to the stone found in Pennsylvania 

 only at that horizon, particularly at the Yardleyville, Newtown and other 

 quarries. The Wilburtha fossils opposite Yardleyville on the Delaware 

 obviously belong to nearly the same horizon. 



The Klinesville fossils come clearly from the Gwynedd shales, appar- 

 ently a little below their middle, and the fossils found near Washington's 

 Crossing and Tumble Station must be from near the top of Ihe same 

 shales. The fossils of Little Falls, Pleasantdale, Feltville, Washington- 

 ville, the Field Copper Mine near Warrenville ("near Plainfield," of 

 Newberry), are all evidently close to one horizon, and that probably in 

 the Lansdale shales near their bottom. The fossils of Martinsville and 

 Pluckamin are perhaps slightly higher up in the same division ; those of 

 "Whitehall and New Providence apparently at about one horizon slightly 

 above the middle of that division, and those of Pompton Furnace still 

 higher towards the top of the division. The fossils of Boonton would 

 seem to be of about the same horizon as those of Mil ford in the Perkasie 

 shales, near the bottom ; and those of New Vernon slightly higher in the 

 same shales. 



It may be noticed that the map represents the trap in place as generally 

 much less extensive than it is commonly given in New Jersey geological 

 maps. It appears to have been customary, both here and in the Connec- 

 ticut Vallej^ to infer the existence of solid trap everywhere beneath the 

 surface exposures of trap bowlders and decomposed trap earth. From 

 observations in Pennsylvania, however, it seems far more probable that 

 the solid trap in place is of much narrower dimensions, as often appears 

 where streams have cut their way through hills. It seems quite natural, 

 too, that so hard a rook as the trap generally is should be left by the ero- 

 sion in the form of hills, standing out prominentlj'' above the neighboring 

 spaces that are underlain by the comparatively unresisting sedimentary 

 rocks, chiefl3'- soft shales. It is also quite natural that abundant remains 

 of broken blocks or bowlders and decomposing earth from the trap, so 

 durable is it, should long exist not only beneath the places where its 

 solid bed once lay, but also be carried by the eroding waters to some little 



