6 TRANSACTIONS OF WAGNER 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
surface is approached. And since a dike or dikes connecting the intrusive with 
the extrusive sheet may well have been removed by erosion or remain hidden 
in the low ground between the hills, this is regarded as the most r 'asonable 
interpretation of the relations in the Jacksonwald area. 
Before leaving the discussion of the geological relations of the trap sheets, 
a word should be said concerning the character of the surface at the time of the 
eruption of the extrusive mass. In Massachusetts and Connecticut there is 
good evidence that the Triassic lavas flowed into deep bodies of water. In the 
case of the First Watchung Mountain in Northern New Jersey it has recently 
been shown that while it flowed over dry land for the greater part of its course, 
there was also a shallow lake, in the vicinity of the city of Paterson, whose waters, 
converted into steam by the intense heat of the molten material, caused a sudden 
cooling and shattering of the latter. Although the extent of the sheets here 
considered is very small compared to some of those in the other places, the 
features shown are none the less interesting. There is not the slightest sign 
of contact of the trap with a body of water, the base being solid and compact 
at every exposure. Moreover, the sediment could not have been in the condi- 
tion of soft mud, as may be seen to be the case below the First Watchung 
sheet at Upper Montclair, New Jersey. There the base of the trap is very 
irregular in outline, while here it is comparatively even and straight, showing 
that the material must have been rather dry and solid at the time of the eruption. 
That the Newark sediments were frequently exposed to the atmosphere is gen- 
erally recognized from the abundance of sun-cracks, but we have here evidence 
that they also became hard and firm at the surface, without requiring to be 
deeply buried beneath subsequent deposits. 
A note should also be added concerning the relations exhibited by the 
other trap masses in the Newark Group in Pennsylvania, for, as appears from 
the conflicting statements concerning them in the literature and from the ex- 
tremely inaccurate manner in which they were mapped by the Second Geological 
Survey of the State, they have received but little attention in the past. In the 
course of the present study practically all of these traps east of the Susquehanna 
River have been examined; they have been found in every case to present 
relations similar to those of the southern sheet in the Jacksonwald area, the most 
striking as well as the most conclusive feature being the metamorphism exhibited 
by the overlying sediments, and are unquestionably to be considered as intrusive 
in origin. The upper sheet at Jacksonwald is apparently the only one in which 
there is the slightest indication of solidification at the surface of the earth. 
