44 J. VOLNEY LEWIS 
of the sedimentation would have its inevitable effect upon the thick- 
ness and distribution of the subsequent deposits. This is particularly 
true of shallow water and continental formations, in one or both of 
which categories the Newark beds must be placed. 
The proposed hypothesis to account for the conditions above 
enumerated in Second Mountain may be stated as follows: After 
the eruption of the trap sheet of First Mountain and the deposition of 
some 600 feet of overlying sandstones and shales, a second eruption 
occurred, forming a lava flow averaging probably 500 feet thick over 
the same region. This is the trap of the outer crest of Second Moun- 
tain. With this outflow began a gradual depression of the southern axial 
region of the great Passaic Basin syncline, the region northeastward 
from Somerville. In consequence of this warping, subsequent deposits 
were concentrated in this region, tending to build it up to the level of 
the adjoining area, but before this condition was finally attained depo- 
SD Wane WD 
ZA SITEEZEZ ZI. WNW Fi 
Sediments AQ Trap 
Fic. 3 
sition was again interrupted by eruption. Another lava sheet of 
about 500 feet average thickness was spread over the region, but not 
uniformly nor even approximately so, as the preceding flow had been. 
Over the shales in the area of subsidence the maximum thickness was 
at least 800 feet, while in the adjoining regions where it rested on the 
unburied flanks of the preceding flow it probably did not exceed 200 
feet in thickness. ‘Thus the two flows, separated by a brief interval of 
deposition, merged into one on the sides of the incipient syncline, 
but were elsewhere separated by a thin stratum of shale. (See section 
Fig. 3.) This refers, of course, to the portions of these sheets still 
preserved to us, all of which are involved in the Passaic Basin syn- 
cline. 
When by later movements their upturned edges were exposed to 
the forces of weathering and erosion, the soft interbedded shales quick- 
ly wore away to a lower level, thus forming the continuous valley curving 
conformably with the outcropping edges of the adjacent trap sheets 
above and below. ‘The valley between the crests of Second Mountain 
eT 
