GEOLOGIC EFFECTS OF THE ICE-SHEET 145 



western half of N6w York the rich display of clrumlins (nearly a thou- 

 sand ridges being shown by the contours on the Palmyra sheet alone) is 

 practically limited to the territory north of the divide, where the drift 

 was profuse and the thinning ice was pushing on an upslope. In the 

 Ontario Basin their attitude or direction of the major axis is radial to 

 the middle of the basin, varying from due east to southwest. In the 

 Erie Basin a group about Chautauqua Lake points southeast, while in 

 the Mohawk Valley north of Richfield Springs a group has westward 

 pointing. In the Champlain and Hudson Valley the drumlins point 

 southward. In the St. Lawrence Valley they show a spreading flow. 

 Everywhere they show the later ice-flow direction. 



The most typical drumlin form, that which seems to express the most 

 vigorous action and effective balancing of the several factors, is an elon- 

 gated oval, with steep convex side slopes, and these are found in the 

 middle of the drumlin belt. New York exhibits all possible variations 

 from this form. The shorter ridges, sometimes approaching dome-shape, 

 but usually with some irregularity or lack of symmetry, are found at the 

 north or proximate side of the drumlin belt, which suggests that the 

 broad form is the product of less perfect work. The much elongated and 

 attenuated ridges lie at the south or ultimate side of the belt, and indi- 

 cate the more uniform or rigid flow of the ice-sheet with deficiency of 

 drift. 



In the western end of the State the till sheet over large areas has been 

 rubbed into a fluted or washboard form on a large scale, but with low 

 relief. It is inferred that this drumlinized surface, with ribs one-fourth 

 to one-half mile wide, represents the work of thick ice having great 

 weight and vertical pressure, with diminished plasticity and carrying 

 only a moderate load of drift. The direction of the flutings, southwest- 

 ward, is the direction of flow of the maximum ice-body. 



In central New York we have been able to definitely correlate the 

 drumlin belt with its synchronous moraine; to determine the position of 

 the ice-front during the drumlin-making episode. On the meridian of 

 Seneca and Cayuga lakes the drumlins of the north side of the belt are 

 more scattering and irregular in form. In the middle of the bolt they 

 are close-set, typical elongated ovals. Soul h ward they become close-sot 

 ridges will) secondary flutings, while at Hie south edge of the bell they 

 are slender ridges and flutings, too attenuated to he represented by the 

 20-foot contours of the topographic sheets. It would require at least 

 5-foot contours to show the frontal drumlinized surface. Two miles in 

 front of the most southerly ridges indicated on the Geneva sheet lies a 



X— Bull. Geol. Soc. Am., Vol. 24, L912 



