Davis and Wood.] 
412 
[Nov. 20, 
movements it has suffered since it was formed ; but we shall not 
now attempt to detect the individual elevations and depressions of 
which the total is composed ; the geological evidence by which they 
may be proved is not yet all worked out, and with exceptions that 
will be mentioned in later paragraphs, the minor oscillations that 
have probably occurred have been without geographic consequences 
recognizable on the maps . 1 
The plain is lowest about Bound Brook, where its interstream sur- 
face averages only about seventy feet over present sea-level ; it 
rises thence to the south, and along the back of Rocky Hill reaches 
one hundred and twent } 7 to one hundred and thirty feet ; from Som- 
erville towards Flemington and White House, it rises from one 
hundred to two hundred feet ; the latter altitude is maintained near 
the Delaware by Lambertville and above Trenton. From Trenton 
across the country to New Brunswick, there is another low strip 
ranging from eighty to a hundred feet ; farther south about Hights- 
town, the surface rises to one hundred and thirty or one hundred 
and forty feet ; near the Atlantic-Delaware divide, the plain is two 
hundred feet above the sea. It appears from this that the Central 
plain is no longer a level or continuous surface. It has been tilted 
and dislocated, its two parts dipping at a gentle angle to the north 
or northwest ; and the step by which they are separated marks the 
location of the fall-line dislocation, as described most fully re- 
cently by McGee, of which more below. It seems to be necessary 
to regard the two parts into which the Central plain is thus divided 
as formerly joining in a continuous surface ; for they are both base- 
levelled plains of post-Cretaceous erosion, and they have both been 
channelled by comparable amounts in later time. If the two parts 
of the country had held their present relative positions while the 
lower part was baselevelled, as it is so perfectly about Monmouth 
Junction, it is impossible that the upper portion could have retained 
as much of its interstream surface unworn as appears around Prince- 
ton. The two parts have been baselevelled together ; their unequal 
heights now indicate subsequent unequal elevation. As the fall- 
line dislocation follows close along the boundary between the Tri- 
assic and Cretaceous formations, the two parts into which the Cen- 
tral plain is now divided may be named after these geological areas. 
J The deltas and shore line deposits of the Columbia formation described by McGee, 
not being represented by special colors on the geological map of New Jersey, are not 
here considered. 
