734 ARTHUR C. TROWBRIDGE 
pull for a horse when one is driving up the upper slopes, but, once 
the top is reached, the road has little grade. This can be well 
seen on the upland over the Great Western tunnel, or on the hills 
around Elizabeth, or almost anywhere on the upland surface. 
Even in the north part of the district the Niagara-capped mounds 
are flat topped, and those which stand in east-west lines come up 
to almost a common level. It is clear that if all the valleys were 
filled up to the tops of the mounds, the resulting surface would be 
nearly flat, and the presumption is strong that there was once a 
plain here which has since been dissected. The mounds in the 
north part of the district reach elevations of 1,170, 1,152, 1,160, 
etc. In the central part, the mounds and the tops of the Niagara- 
capped ridges reach 1,112, 1,145, 1,005, 1,000, 1,072, etc. Im the 
south portion of the district, considerable areas of the plain are 
found at 944, 964, 1,027, 1,004, and 1,000 feet. That is, if this 
plain were reconstructed, it would slope south and southwest about 
175 feet in 16 miles, or about 11 feet to the mile. In Wisconsin, 
a few miles north of this district, this same surface on the Niagara 
dolomite reaches elevations of 1,400 feet, showing a continued rise 
in that direction. It is seen then that this plain, if reconstructed, 
would slope in the direction in which the rock strata dip and at 
about the same angle. 
The origin of this-plain is now in auecaon There are at least 
four possibilities: (1) it is an old peneplain uplifted and dissected 
after its formation by streams; (2) it is a plain made by a hard 
layer of rock at this stratigraphic horizon; (3) it is the original sea 
bottom which, after emerging, remained low and flat for a long time 
after the Niagaran epoch; or (4) it is the result of the erosive 
action of ocean waves cutting back on the land, at a time subsequent 
to the deposition of the Niagara dolomite and any other formations 
which may have been laid down on it, the present remnants result- 
ing from the partial erosion of the surface by streams following 
uplift relative to the sea. The correct one or ones of these four 
hypotheses ought to be determinable by close field observation. 
t. If such a flat is a dissected peneplain, (a) it is likely to have 
hills standing above it, which were left unreduced in the former 
cycle of erosion; (0) the surface is likely to have some relief; (c) the 
