108 D. F. Lincoln — Glacial Erosion of New York. 



and larger forms of the parts nearer Lake Ontario. The mate- 

 rial of these small drumlins, if spread over their own neighbor- 

 hood, would not exceed 10 or 20 feet in thickness. 



Kames' and osars have been observed in three counties, but 

 not with sufficient system to enable an estimate to be offered. 

 It is not believed that the material they contain would add 

 very greatly to the total. 



The deepest parts of the lakes may be assumed, with proba- 

 bility, to be nearly free from drift. On the south they are 

 prolonged in alluvial plains, reaching several miles, which may 

 not be all Post-glacial. The northern ends of several lakes 

 also appear to be choked with Glacial deposits. At Geneva 

 several wells have been sunk at the water's edge, passing 

 through gravel, sand, clay, and till, with many large bowl- 

 ders, and striking bed-rock at 205, and 240 (?) feet. Ad- 

 jacent drumlins rise to the height of 90 feet. A mile from 

 the lake, at an elevation of 100 feet, the drift is 60 feet thick ; 

 half a mile further, on higher ground, shale crops out in seve- 

 ral spots. This drift-mass extends six or eight miles to the 

 southward, occupying the width of a, mile on the west bank 

 of the lake, and very probably shoaling a corresponding por- 

 tion of the lake. On the whole, it may be estimated that -| of 

 the surface of land lying between the Finger Lakes and extend- 

 ing to (but not including) the terminal moraine, is covered 

 with drift, averaging from 1 to 5 feet in thickness. Another 

 -f may average from 5 to 30 feet. The remainder may be 

 included, for the most part, between 30 and 100. 



In close connection with the above study, a question of great 

 interest awaits solution — that of the origin of the trough-like 

 lake-basins. The reader will not fail to recall the diversity of 

 opinion, which has been recently developed by the discussions 

 upon the origin of mountain lakes, in the pages of " Nature " 

 for 1893. It is not my present purpose to enter into this dis- 

 cussion. Certain facts, however, in part new, may well be 

 mentioned here, as deserving to be weighed before we take 

 sides. In part, these favor the theory of deepening by Glacial 

 erosion ; in part, that of tilting or differential uplifts, whereby 

 valleys that once ran continuously to the sea have been bent 

 so as to hold water like a spoon. For the sake of simplicity, 

 let us confine the presentation to Seneca Lake, which will serve 

 as a type. Situated in the axis of the system known as the 

 Finger Lakes, this valley has been cut down to a depth con- 

 siderably greater than either of its neighbors ; in addition to 

 which, it is the one about whose rock-contours we have most 

 definite information. We will consider it as incidental to a 

 valley, 58 miles long, running from the flat land at Geneva 

 south to a junction with the Chemung Yalley at Elmira ; of 



