THE GEOLOGICAL HISTORY OF NEW YORK STATE 21 
Falls and “ The Noses” (Yosts), the river has cut down to the Pre- 
cambric (Adirondack) rock. In general, the rock formations of 
the province tilt slightly southwestward and show folding only on 
a very small scale. From Little Falls eastward, however, the strata 
are greatly disturbed by numerous nearly north-south faults which 
are often of considerable magnitude (see figure 25). 
ERIE-ONTARIO PLAINS PROVINCE 
On the extreme western side of the State, and lying between 
Lake Erie and the Southwestern plateau, there is a strip of land 
only a few miles wide which may be called the Erie plain. This 
plain is of very low relief and slopes from an altitude of from 
800 to goo feet down to the level of Lake Erie, whose altitude is 
573 feet. Where the Erie plain joins the Southwestern plateau 
there is a very decided change of slope. The rocks underlying this 
plain are dark shales of Devonic age and show the usual slight 
southwestward tilt (see plate 31). 
The Ontario plain is much larger and lies between Lake Ontario 
and the Southwestern plateau, the southern boundary being marked 
by the ‘Helderberg escarpment.” This large province slopes 
gradually to the shores of Lake Ontario and is remarkably free 
from relief features of any considerable magnitude. One that 
deserves mention is the presence of many hundreds of low, glacial 
knobs (drumlins) which are thickly scattered over the whole plain 
-between Rochester and Syracuse (see plate 42). Another feature 
which serves to break the monotony of the plain on the west is the 
low but distinct escarpment of Niagara limestone, which extends 
from Lewiston eastward to beyond Lockport. On the east the 
Ontario plain gradually merges into the Mohawk valley province 
on the one hand, and on the other hand comes against the western 
foot of the highlands of the Tug Hill province. 
The rocks underlying the Ontario plain are chiefly sandstones, 
limestones and shales of Siluric age, which show the usual tilt 
toward the south. At the extreme northeast, limestone and shale 
of Ordovicic age are present and these show a slight westward tilt. 
TUG BILL PROVINGE 
The Tug Hill region is worthy of recognition as a distinct physio- 
graphic province because we have here a highland mass of con- 
siderable extent entirely separated from the neighboring provinces. 
The highest point, six miles west-northwest of Lyons Falls, Lewis 
