Febeuaet 14, 1913] 



SCIENCE 



245 



iee accepts a thrustal movement, producing 

 a sliding motion of the ice in ground-con- 

 tact; (4) such temperature or physical con- 

 dition as to allow plasticity and some differ- 

 ential motion within the ice, essential for 

 the overriding of the growing obstruction 

 instead of its removal. Here is found a 

 singular balancing of two opposing factors, 

 rigidity and plasticity ; rigidity holding the 

 iee mass, as a whole, to its thrustal motion, 

 while at the same time bands or currents 

 within the ice sheet have unequal motion, 

 permitting the curving or arching flow 

 over the growing hill of drift. The 

 drumlin-making process appears to be a 

 plastering-on and a rubbing-down, depend- 

 ing on the condition of more friction be- 

 tween clay and clay than between elay and 

 ice. The resulting form of the growing ob- 

 struction is that which offers the greatest 

 resistance to removal, or the least resistance 

 to the passage of the ice over it. The mold- 

 ing action of the ice sheet is well shown by 

 the minor ridges in some districts, the sec- 

 ondary and tertiary inferior ridges lying 

 on the flanks of or between the primary 

 ridges suggest the wood-molding struck in 

 the planing mill. 



The complex of forces and conditions 

 necessary for drumlin construction ex- 

 plains their peculiar distribution, ozienta- 

 tion and form. In the western half of New 

 York the rich display of drumlins (nearly 

 a thousand ridges being shown by the con- 

 tours on the Palmyra sheet alone) is prac- 

 tically limited to the territory north of the 

 divide, where the drift was profuse and the 

 thinning iee was pushing on an upslope. 

 In the Ontario basin their attitude or direc- 

 tion 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 Rich- 

 field Springs a group has westward point- 



ing. In the Champlain and Hudson valleys 

 the drumlins point southward. In the St. 

 Lawrence Valley they show the latest and 

 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 elongated oval with steep con- 

 vex side slopes, and these are found in the 

 middle of the drumlin belt. New York ex- 

 hibits all possible variations from this 

 form. The shorter ridges, sometimes ap- 

 proaching 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 indicate the more uniform or rigid flow 

 of the iee 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 ver- 

 tical 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 maxi- 

 mum iee 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 drum- 

 lin-making episode. On the meridian of 

 Seneca and Cayuga lakes the drumlins of 

 the north side of the belt are more scatter- 

 ing and irregular in form. In the middle 

 of the belt they are close-set, typical, elon- 

 gated ovals. Southward they become close- 

 set ridges with secondary flutings ; while at 



