1889.] 
379 
[Davis and Wood 
as these be developed? A geological examination of the district 
leads to the conviction that the trap-sheets, like the sedimentary 
beds between them, have formerly had a great extension upward 
along the plane of their dip into the air, just as they still have an 
undetermined extension downward into the ground ; their present 
edges simply mark the lines back to which the sheets have been 
consumed by denuding forces of one kind or another. If the land 
had stood at its present altitude during the long time needed for 
the consumption of the lost portion of the sheets, the long, level 
crest-lines between the transverse gaps could find no explanation 
in accordance with the general laws of land-sculpture, as the}' are 
at present understood ; they might in such case be rounded, as in 
fig. 3a, but could not be even, as the}' are shown in fig. 36. The 
Fig. 3a. 
Fig. 3b. 
only satisfactory explanation of their evenness is to be found in the 
supposition that their crests are remnants of a plain of baselevel 
denudation, formed when the land stood lower than now. The val- 
leys between and alongside of the parallel ridges, and the trans- 
verse gaps that cross them, have been worn out since this plain 
was elevated to about the height of the present crest-lines. 
Several other trap ridges of similar form call for a similar ex- 
planation. Sourland and other ridges in the southwest, Rocky Hill 
on the south, and the Palisades on the east all have tolerably even 
crest-lines, and are presumably remnants of extinct plains that 
once stretched away to either side of the ridges at the level of their 
tops. 
It may be reasonably inquired whether these extinct plains were 
not, at the time of their fullest development, parts of one and the 
