294 Tertiary. 



and spread over the bottom in shallow water near the shore. In higher 

 situations, and just beneath the great limestone terrace thej' 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 b}^ the passage of the Hamilton Group to 

 the rocks above; and in all the previous cases, the}' 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 finall}' toward 

 the southern margin of the State they are rarely seen. 



Some of them bear evidence of much wearing, being 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 evi- 

 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. Man}' of them ai-e 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 lakes 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 crj'S- 

 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 vallej's, piling up the coarser ma- 

 terials at the northern extremity, and moving the finer ones farther on. 



