16 NEW YORK STATE MUSEUM 
region, and great masses of igneous rocks have been forced through 
these. All these rocks have been subjected to tremendous earth 
pressure which has folded and thoroughly metamorphosed them. 
SOUTHWESTERN PLATEAU PROVINCE 
This, the largest clearly defined phystographic province, occupies 
nearly one-third of the area of the State. The rocks are all 
unaltered sediments of Devonic age, except a few small patches 
of Carbonic rocks in the southwest, and consist of shales, sandstones, 
and conglomerates. These formations exist as vast sheets or layers 
piled one upon another, with an aggregate thickness of several thou- 
sand feet (see figures 3 and’5). In marked contrast to the Adiron- 
dack province, the rock masses of this southwestern plateau are 
practically devoid of displacements, the only disturbance being a 
slight tilt (30 to 50 feet a mile) of all the strata to the south or 
southwest, associated with low northeast-southwest undulation. 
Although this plateau is pretty well trenched or dissected by 
streams, it is nevertheless not a mountainous country, there being 
no high ranges or peaks standing out prominently. The elevation 
of the province varies from 500 to 600 feet on the northern side 
to over 2000 feet on the eastern and western sides. A notable 
feature is the distinct sagging of the plateau toward the middle 
portion. This sagged or depressed portion is occupied by the Finger 
Lakes, especially that portion filled by the south ends of Cayuga 
and Seneca lakes and the valleys which-enter them from the south 
in the region of Chemung and Tioga counties. It is possible, by 
traveling along Seneca lake and thence southward to Elmira and 
the Chemung river, to pass entirely across the plateau province 
from north to south without attaining an altitude of much over 
goo feet, which is on the divide between Watkins and Elmira. 
Physiographically, the Plateau province is really but the north- 
ernmost extension of the great plateau which lies along the western 
base of the Appalachian mountains. On the east the province is 
bounded by the Catskill mountains which are in no sense sharply 
separated from the plateau itself. On the west and north the 
province is bounded by the Erie-Ontario plain and Mohawk valley 
provinces. The northern limit is pretty clearly marked by what 
is known as the “ Helderberg escarpment’ of Devonic limestone. 
This limestone, being of considerable thickness and more resistant 
than the neighboring formations, has generally stood out boldly 
against erosion, thus causing an abrupt change in relief. The 
escarpment is particularly prominent along the boundary of the 
