385 
[Davis and Wood* 
ern extension below sea-level, where certain stratified deposits of 
later date conceal the depressed middle portion of the Palisades- 
Rocky Hill trap sheet about New Brunswick ; the same deformation 
has lifted the western part to a height that allows the excavation 
of deep valleys below the old baselevel surface. 
Several questions now arise. We may ask the geologic date of 
the completion of the Schooley baselevelling, in order to associate 
it properly with other topographic features of the same age. We 
may inquire into the geographic conditions of the origin of the 
stratified .deposits that now bury the Palisades-Rocky Hill trap 
sheet, and ask if they give indication that the eastern part of the 
Schooley peneplain is a platform of submarine origin. The fur- 
ther original extension of the same deposits to the northwest must 
be considered, in so far as they may have had geographic conse- 
quences in controlling the development of our existing stream- 
courses. Finally, the date of the elevation of the Schooley pene- 
plain must be discovered, in order to gain some comprehension of 
the rate of subsequent geographic growth, measured in geologic 
units. 
18. Date of the Schooley baselevelling. The general sequence of 
events by which the geological date of the Schooley baselevelling 
is determined is as follows. The great Appalachian revolution cul- 
minating in Permian time produced a mountain range of strong con- 
structional relief, and presumably of strong actual relief for a cer- 
tain period after the disturbances. But in the area occupied by the 
Triassic belt, the topography seems to have been reduced to a 
moderate relief before Triassic deposition began ; this we know be- 
cause the southeastern margin of the Triassic formation, where it 
joins with older rocks, is a rather even line across the Triassic-Cre- 
taceous peneplain of to-day. From this it must be concluded that 
the foundation on which the Triassic beds lie is also a peneplain, 
the product of pre-Triassic erosion on a mass of mountainous 
structure. The great mass of sediments accumulated in the Tri- 
assic cycle has suffered tilting and probably faulting also, and there 
is good reason to think that this disturbance extended over a con- 
siderable area on either side of the present Triassic belt : this pro- 
duced a new mountainous topography, of less elevation and of much 
less structural distortion than that of Permian time, but still of con- 
siderable strength, as suggested in paragraph 12 ; and it is the 
old age of the forms of this cycle of development that we have de- 
PROCEEDINGS B. S. N. H. VOL. XXIV. 25 MARCH, 1890. 
