DRUM LI Xs. 



291 



ion that drumlins were formed, in a way "similar to that by 

 which a stream of water often makes longitudinal ridges of 

 sand in its bed.''* This is to 

 my mind the best suggestion yet 

 given to account for them. 



J. Geikie wrote as follows : 

 "The remarkable linear direc- 

 tion of certain mounds of bowl- 

 der-clay in some districts of the 

 Lowlands, agreeing as this does 

 with the general bearing of gla- 

 cial markings of the same lo- 

 calities, induces us to believe 

 that we have here, with certain 

 modifications, the original con- 

 tour of the till after the super- 

 incumbent ice-sheet had disap- 

 peared " ; f but he believed that 

 these forms may be also in part 

 dependent on marine erosion. 

 In the "Great Ice Age," the 

 same author briefly mentioned 

 "the series of long, smoothly 

 rounded banks or drums, and 

 sow-backs, which run parallel 

 to the direction taken by the 

 ice," and regarded them as very 

 little modified from their glacial 

 form. They are "produced by the varying direction and un- 

 equal pressure of the ice-sheet," and are "the glacial counter- 

 parts of those broad banks of silt and sand that form here and 

 there upon the beds of rivers." Dr. L. Johnson says that he 

 accepts Geikie's explanation, and applies it to the New York 

 ridges which were "formed underneath the glaciers by alterna- 

 tions of lateral pressure " ; but this form of statement does not 

 commend itself so highly as the preceding. 



Fig. 93.— Drumlins in Ireland, after Kin- 

 nahan and Close. (.Davis.) 



* "General Glaciation of Iar-Coiinaught," Dublin, 1872. 



f "Transactions of the Geological Society of Glasgow," vol. iii, 1867, p. 61, 



