190 Cincinnati Society of Natural History. 
and spread over the bottom in shallow water near theshore. In higher 
situations, and just beneath the great limestone terrace they again ap- 
pear in abundance, as if this elevation prevented their farther advance 
to the south. The bowlders are most abundant in Wayne and the 
eastern part of Monroe county; going westward from the Genesee 
they are less so, becoming extremely rare in Erie and Niagara counties, 
As we ascend the second limestone terrace formed by the Helderberg 
range of limestones extending westward, bowlders become perceptibly 
less numerous; they are irregularly scattered, and at few points pre- 
sent the thickly covered fields which are observed farther north. Very 
few ascend the slope formed by the passage of the Hamilton Group to 
the rocks above; and in all the previous cases, they seem to have been 
brought on, at intervals, in great numbers, and their limits bounded by 
the different elevations of the surface. As we pass southward over the 
higher groups, bowlders become exceedingly rare; and finally toward 
the southern margin of the State they are rarely seen. 
Some of them bear evidence of much wearing, heing actually striated 
upon the surface, and sometimes flattened on one side, as if held in 
that position while moved over a bottom of gravel or sand resting up- 
on the strata beneath. For the most part, however, they bear no eyvi- 
dence of attrition beyond what similar masses do a few miles from 
their parent rock, and thus offer no argument for their mode of trans- 
portation. Many of them are angular, and with no appearance of at- 
trition beyond what the weathering in their present situations would 
produce. The process by which fragments of granite become rounded 
bowlders, is illustrated by the desquamation which takes place in some 
granites, the weathering in place, and the attrition in mountain streams 
soon after leaving their native beds. A large proportion of the bowl- 
ders of western New York are of dark felspathic granite and red gran - 
ites like those of the northern part of the State. Some other varieties 
occur, which are likewise referable to the same region. A few of crys- 
talline limestone with serpentine, and a few of specular iron ore have 
been found which are like rock found in St. Lawrence county. 
In many places, the drift hills have no definite direction, but those 
north of the great valleys of Seneca and Cayuga lakes are long ele- 
vated ridges, rising abruptly on the north, to a height of 50 or 60 feet, 
and sloping gradually down to their southern termination. The form 
of the hills is precisely such as would be made by a powerful current 
passing southward through these valleys, piling up the coarser ma- 
terials at the northern extremity, and moving the finer ones farther on, 
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