244 J. D, Dana on a Mohawk-valley Glacier. 
eet. It is not a synclinal valley; neither is it a valley of de 
nudation, although, beyond doubt, greatly deepened and ex- 
tended by the action of waters; but it is what the writer has 
styled a geoclinal valiey, that is, one formed by the uplift of the 
crust of the earth on either side, (or else by the depression of the 
crust along its course,) without any conformity to its slopes m 
the dip of the enclosing rocks.’ These enclosing’ rocks of the 
Mohawk depression are in fact, on one side, partly (above @ 
height of a few hundred feet) the folded and crystallized Azoie, 
and, on the other, the Paleozoic rocks which were uplifted at a 
much later period. 
About midway between Albany and Rome, the valley-depres: 
sion, taking only the part south of the Mohawk, measures, at a0 
elevation of 1500 feet, ten or twelve miles in breadth. But just 
east of this in Schoharie county, it opens southward along the 
valley of the Schoharie creek, the principal southern tributary 
of the Mohawk. This Schoharie valley is bounded, on the west, 
by the northwestern prolongation of the Catskill Mountains, 
having here a height of 2000 to 2600 feet above the sea level; 
on the east, by a spur from the same mountains, called the Helle- 
bark mountains, which increases in height southwardly from 
1000 to 2000 feet, and at whose eastern foot, in Albany county, 
lie the Helderberg hills, 800 to 1200 feet high above the sea-level. 
The principal heights of the Catskills, between 3400 and ¢ 
feet in altitude, are situated to the south, not far from the Jus 
tion of the two ridges. The range of the Catskills has a height 
at the Mountain House, according to Guyot’s measurements, © 
e and eastward to the Hudson. " 
On the north side of the Mohawk, land 1500 feet in elevation 
is not met with except at very distant points from the river 
in the Black river region, towards Lake Ontario, which has t 
height, and in the Adirondack region, towards Lake Champlai3, 
whose highest peak, Mt. Marcy, runs up to 5379 feet. ; 
The Mohawk valley is continued westward in the depress pr 
* The word geoclinal is derived from the Greek yy earth and xawo I incliné- 
The Connecticut, Hudson, and Mississippi are other geoclinal valle: 
