196 ROCHESTER ACADEMY OF SCIENCE. 



( 19) Amount of material on the Malaspina glacier cannot be 

 taken as an index of the surface conditions of continental glaciers, 

 for much of the superglacial material of the Malaspina is due to 

 avalanching. 



(20) Not enough debris would be brought in after the super- 

 glacial stream had reached the graded condition necessary to deposi- 

 tion to build eskers possessing such large dimensions as are fre- 

 quently observed. 



(21) Warm waters would have to penetrate deposits 50 or 

 more feet thick and warm the ice beneath sufficiently to melt it. and 

 in the case of broad eskers and "plains" penetrate a deposit of 500 

 feet or more wide and 25 to 100 feet or more thick, apparently an 

 impossibility. 



(22) Superglacial streams must always have had an obstruc- 

 tion at their mouth to permit aggradation, otherwise they would not 

 have reached grade till the stream bottom rested upon the ground. 



23) Shearing is little effective in getting material up into the 

 ice, it is opposed by basal drag of the ice and the resulting more rapid 

 movement of the upper portions of the ice. 



Conclusion. Of the numerous objections noted several appear 

 to be absolutely fatal to the theory and preclude the possibility of 

 the majority of eskers having been formed in this manner. The 

 local character of the esker materials, the confinement of debris to 

 the basal portion of ice masses, the swiftness of superglacial streams, 

 their smooth channels and short lengths, and the difficulty of getting 

 ridges so formed down upon the ground without their destruction, 

 are perhaps the most serious difficulties in the way of acceptance of 

 the theory. A well known glacialist once remarked in the presence 

 of the writer, "no one who has ever visited an ice sheet would enter- 

 tain for a minute the idea of superglacial origin of eskers." 



Hypothesis of origin at the edge of the ice. Baron De Geer of 

 Sweden early stated his conviction that eskers were laid down 

 where a glacial river emerged from the ice sheet and deposited its 

 material as a fluvio-glacial fan. As the ice front receded the deposits 

 of successive years formed a continuous gravel ridge, which fol- 

 lowed the retreating mouth of the river. 



Hershey in his study of Illinois eskers seems to have come to a 

 similar conclusion regarding their origin (48). He thinks that the 



