DRUMLINS OF CENTRAL WESTERN NEW YORK 429 



moved or slid by shearing; but this could hardly apply to the Clyde 

 and Montezuma districts, where the drumlin forms lie at the lowest 

 levels. 



A modification of the subglacial drainage theory offers some help. 

 It seems probable that the last stage of the glacier in this region left 

 an extensive border tract of stagnant ice, and that unequal melting 

 due to a variety of causes produced detached blocks or tracts of ice 

 around or among which the copious glacial waters excavated many 

 channels. The subglacial drainage combined with the later inter- 

 ice block drainage may largely account for the peculiar features. 

 In this connection it must be understood that the attitude and 

 elevation of the land surface of the region has changed to some 

 extent since the features were made; and that the lakes and slug- 

 gish waters, aided by organic growths, have partially filled the low 



grounds. 



Summary 



Age of the drumlins. The form and relations of the drumlins 

 in the Pulaski district, due to the change of direction in the ice flow 

 proves that they were shaped during the latest phase of the ice work 

 in that locality, and not during any earlier stage. The same conclu- 

 sion is reached by the theoretical considerations and enforced by 

 the facts of observation for the entire drumlin area. 



The peculiar distribution of the drumlins and their orientation 

 prove that they were shaped by the spreading flow of the semistag- 

 nant ice mass reposing in the Ontario basin. The correlation of 

 moraines and of ice border drainage channels with the attenuated 

 edge of the main belt of drumlins indicates that the drumlins were 

 formed beneath the border of the ice sheet. This correlation of the 

 drumlin shaping with the latest work of the ice in the drumlin region 

 has been noted in other drumlin areas, as Wisconsin, Massachusetts, 

 Ireland and Germany. The fact seems to be sufficiently established 

 that the alinement and shaping of the drumlins was given under the 

 waning border of the ice sheet, at least m the case of the continental 

 glaciers. 



Thrust motion of the ground contact ice. Drumlins are 

 shaped by the sliding movement of the lowest ice, that in contact with 

 the land surface. This fact implies that the whole thickness of the 

 ice sheet participated in the motion. Such motion was not due to 

 gravitational stress on the ice mass over the drumlin area, because the 



