Geology of Seneca County. 71 



The map of the drumlins here given (fig. 12), is a reproduc- 

 tion from a map of Seneca county, made in 1852, by William T. 

 Gibson, surveyor, known by repute as a careful, painstaking and 

 accurate man. So far as I have been able to compare his work 

 with observations of my own, it is correct ; and as a whole it 

 certainly gives a clear and faithful idea of the singular topog- 

 raphy of the country. The meridian line crosses the ridges at a 

 small angle. It is not asserted that all these hills are of till. 

 Of many that have been inspected, one has been found to consist 

 of sand and gravel along its southern half, as indicated. The 

 kame hills are omitted ; they are very complicated and are not 

 well given by Mr. Gibson. 



Sand Ridges. 



The association of sand with these ridges deserves attention. 

 Light deposits of sand and gravel are frequent on their summits, 

 as is the case in New England, and would suggest that at some 

 stage (probably quite late in the disappearance of 'the ice sheet) 

 super-glacial streams flowing southwards frequently occupied 

 crevasses in the ice coinciding with the tops of the ridges. 

 Physical reasons might be suggested for the preference of ice- 

 crevasses for the tops of earth ridges. 



At Mr. David H. Evans's, in the northeast corner of Tyre, is 

 a ridge, proved by the catting, to consist of till, at least at that 

 point. The outline of the ridge is unlike that of a typical drum- 

 lin, it being carved deeply and irregularly by water to the north ; 

 but southward it develops to a straight ridge, becoming very 

 sandy and yielding, with a parallel ridge adjoining, of similar 

 nature, quite humpy and irregular, with axis about N. 5° W. 

 magnetic. 



A couple of miles north of Seneca Falls village, west of Black 

 Brook, the road partly follows a train of sand deposits which 

 runs two miles to the fetate road, east of Magee's. The direction 

 taken, on the whole, is N. 5° W. magnetic. It begins southward 

 in low sand hills, nearly continuous, which diverge from the line 

 of road and become higher at a point where excavated for sand 

 and gravel. Here they form a group of hills some 20 f et t 

 above the plain. The continuity is interrupted northward for 



