136 JV. II Da/rton — Trap of New Jersey. 



sheet, and he stated his opinion that it conld only have been 

 formed on the surface of a p re-existent sheet of lava. 



The writers studies extending over the entire Newark area 

 in New Jersey confirm Davis's suggestion and give rise to the 

 following conclusions : The extrusive sheets, contemporaneous 

 with the enclosing strata, include all the outcrops constituting 

 the First and Second Watchung or Orange Mountain, and the 

 ridges enclosed between them and the Archaean highlands, and 

 the outlying outcrops near New Germantown. The intrusive 

 sheets comprise those constituting the Palisades, Sourland 

 Mountain, Cushe.tunk and Round Mountains, Lawrence Brook 

 — Ten Mile Run Mountain — Rocky Hill— Pennington Moun- 

 tain — Bald Pate and Jericho Hill series, and the outcrops at 

 Point Pleasant, Snake Hills, Arlington, Martin's Dock, jSTe- 

 shanic, Belle Mountain, Granton and Brookville. 



The extrusive sheets are characterized by their perfect con- 

 formity to the underlying strata, the deep vesicularity and 

 alteration, or slag like aspect of their upper surfaces, the unal- 

 tered and undisturbed condition of the enclosing strata the 

 presence of trap breccias at the contacts, the altered and fre- 

 cmently vesicular condition of the rock at their bases, the evi- 

 dence of successive flows, their relations to anterior tuff de- 

 posits and their distinctive columnar structure and petrography. 



The intrusive sheets are characterized by irregular lower con- 

 tacts in which the trap cuts across the ragged edges of the 

 strata for greater or less distances, the intense alteration in the 

 enclosing strata, the increased density and fineness of grain and 

 the bedded structure in the trap near the contacts, and the ab- 

 sence of vesicularity and breccias. 



In the "Watchung Mountains, erosion, glaciation and drift 

 cover cause scarcity of outcrops of the original upper surfaces, 

 but there are man} 7 localities scattered along their course in 

 which deeply vesicular trap is exposed, and others in which 

 unaltered and undisturbed strata outcrop very near the contact. 

 The only actual overlap well exposed is in the ravine at Felt- 

 ville, where the trap surf ace is in greater part vesicular and slag- 

 like and the soft, red, argillaceous shales fill the irregularities, 

 excepting at one point where there is an intervening trap brec- 

 cia filling the interstices in a slag-like portion of the surface. 

 Contacts of the Watchung traps with underlying strata are ex- 

 posed at intervals along the outer sides of the ridges and abso- 

 lute conformity prevails throughout. The trap is frequently 

 vesicular and altered and lies on the unaltered or very slightly 

 altered strata along a straight or gently sinuous line, in one case 

 with a trap breccia intervening. At two points in its course 

 the second Watchung trap is exposed overlying beds of loose 



