THE GHOLOGICAL HISTORY OF NEW YORK STATE IQ 
escarpment, standing out abruptly and to a great height, forms a 
sharp boundary. On the eastern side the Catskills present a very 
steep, high front facing the Hudson valley. This steep front rises 
about 3000 feet and consists of hard Devonic sandstones and con- 
glomerates overlying the Siluric strata (see figure 6). 
MOHAWK VALLEY PROVINCE 
The Mohawk valley province, though comparatively small, is of 
great importance because it so clearly separates the Adirondack 
highlands on the north from the highlands of the Catskills and 
southwestern plateau provinces on the south. In fact it should be 
noted that the Mohawk valley is by far the lowest passageway across 
the mountains between the St Lawrence river and the southern end 
of the Appalachian range. This low pass is one of the great eastern 
“ gateways ” which, with the St Lawrence, have afforded the easiest 
means of communication between the Atlantic seaboard and the 
region west of the Appalachian mountains. 
The comparatively narrow inner valley through which the river 
now flows is often erroneously called the Mohawk valley, but in 
reality the whole depression, from 10 to 30 miles wide and fully 
1000 feet deep, between the northern and southern highlands of 
the State, should be called the Mohawk valley. At Little Falls the 
inner valley narrows to a gorge several hundred feet deep, where 
the river has cut its way through a preglacial divide (see plate 7 
‘and figure 7). Had it not been for the recent cutting of this gorge 
(see explanation accompanying plate 44 in chapter 6) through the 
barrier at Little Falls, the Mohawk valley would never have been so 
important as a great gateway between the Atlantic coast and the west. 
Today the four tracks of the New York Central Railroad, two tracks 
of the West Shore Railroad, the Erie canal (now being enlarged to 
the Barge canal), an important highway, many telegraph and tele- 
phone wires, and the Mohawk river all pass through this narrow 
gorge and within a few hundred feet of sea level. Eastward and 
westward from Little Falls, the inner valley is generally fairly wide 
and open (see plate 7). At Little Falls the Mohawk river is less 
than 400 feet above sea level and even at Rome, in the western 
part of the province, the river shows an altitude of only 420 feet. 
The principal rocks of the province are shales, sandstones and 
limestones of Cambric and Ordovicic ages; of these the soft, black 
shales of Trenton, Utica, and Frankfort ages are in greatest 
abundance. The valley owes its existence largely to the presence 
of this belt of soft shales lying between the hard crystalline rocks 
