1893] UPHAM ESKERS NEAR ROCHESTER, N. Y. 193 



ester and Pittsford eskers were formed, the ice-melting was likewise 

 promoted by the incipient Lake Iroquois, outflowing by Rome to the 

 Mohawk and Hudson. 



According to notations of glacial striae by Chamberlin, Gilbert, 

 and Dryer, their courses are as follows : near the northeast corner of 

 the city of Rochester, S. S. W. to S. W. ; near the southwestern bound- 

 ary of this city, S. W. to W. S. W.; and in Greece, the next township 

 northwest of Rochester, four courses, intersecting or on contiguous 

 rock exposures, S. S. E., S. S. W., S. W.,and W. The southward courses 

 are doubtless somewhat earlier than those running to the south- 

 west and west, which belong to the short time when the glacial cur- 

 rents were deflected during the departure of the ice. Upon all the 

 region of the Finger lakes the glacial striation is approximately from 

 north to south, in parallelism with these lakes and the intervening 

 ridges and plateaus. On the north the grand ice currents over the 

 Province of Ontario moved mainly southward, with convergence 

 from the southern part of Georgian Bay southeasterly, and from Mon- 

 treal and the upper St. Lawrence southwesterly, toward the basin of 

 Lake Ontario and the great re-entrant angle of the glacial border at 

 Salamanca in southwestern New York. 



The trends of eskers and drumlins testify of the directions of the 

 currents of the ice-sheet as trustworthily as the courses of glacial 

 striation on the bed-rocks, with which, the esker and drumlin ridges 

 are parallel. Both these classes of drift accumulations, however, were 

 formed near the border of the ice during its recession at the close of 

 the Glacial period ; and they consequently often record local deflec- 

 tions of the glacial currents caused by unequal rates of melting and 

 the resultant sinuosities of the ice-front. The Pittsford esker series, 

 trending south-southeast, is nearly parallel with the general move- 

 ment of the ice-sheet, both during the time of its maximum extent 

 and thickness and during the decadence ; but the Pinnacle hills, trend- 

 ing west- southwest, show that a considerable local indentation or 

 embayment in the waning ice-border there turned its currents much 

 to the west from their former course. 



Probable Origin of these Eskers. 



Although these two esker series, lying only a few miles apart, 

 differ about 90"^ in their trends, they were probably formed at the 

 same time or one very soon after the other, as might happen by diver- 



li, Pkoc, Rikh. Acad, of Sc, Vol. 2, April, 1893. 



