July 14, 1911] 



SCIENCE 



61 



causes, while the above concentering ice flow 

 at the bottom continued. Meanwhile the gen- 

 eral advance of the remains of the ice sheet 

 had not entirely ceased and this movement 

 exerted a modifying influence in producing 

 the surface forms that eventually resulted. 

 Finally, as the ice faded away and the water 

 drained off the englacial matter was quietly 

 laid down in the smoothly rounded hills and 

 ridges with intervening plane or hollowed 



7 *iji.^i^Jv>-> 



in and under the ice by the movements de- 

 scribed, and what may be termed its precipi- 

 tation as the ice and water disappeared by 

 melting and slow drainage respectively, were 

 the principal formative causes. If the drum- 

 lin area was subsequently again covered by 

 ice, this was probably of moderate thickness 

 and was formed largely in place by accumula- 

 tion of local snow fall in excess of the rate of 

 melting, with a limited forward movement of 



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surfaces that constitute the hitherto mysteri- 

 ous drumlin topography. 



The forms of these surface features are 

 doubtless attributable in some degree and in 

 certain localities to the direct action of over- 

 moving ice, either during formation or sub- 

 sequently, but it seems probable that the 

 gathering up of the drumlin material while 



the sheet; the effect on the surface being like 

 laying down a heavy blanket over it and then 

 dragging the blanket forward, rather than 

 like pushing over the area a thick ice sheet 

 with a definite front edge. 



The original forms of the drumlins appear 

 to have been remarkably preserved since the 

 ice period by the conditions of soil and climate 



