SoLLAS — A Map to show the Distribution of Eskers in Ireland. 799 



of the eskers to a winding river ; the esker described by Mr. Ells runs along with 

 the Hebert River, which is considered to have had some share in its formation. 

 Mr. Chalmers attributes the kames observed by him to post-glacial streams. 



There is a short reference to eskers by Professor Shaler in 1889* ; it is chiefly 

 interesting for its virtual retractation of his earlier views, and the statement that 

 he regards eskers as formed within sub-glacial channels during the last stages of 

 the melting of the ice-sheet. 



Numerous eskers and kames are described by Mr. Warren Upham in different 

 parts of Minnesota, t and referred to the action of streams flowing through canons 

 in the ice. 



A very welcome addition was made to our knowledge in 1890 by Professor 

 G. F. Wright in his work on The Ice Age in North America (Kegan Paul & Co., 

 London), containing (p. 62) a description of eskers actually in process of formation. 

 It runs as follows : — 



" Now that the front is retreating, this sub-glacial stream occupies a long 

 tunnel, twenty-five or thirty feet high, in a stratum of ice which is overlaid to a 

 depth, in some places, of fifteen or twenty feet with waterworn glacial debris. In 

 numerous places the roof of this tunnel has broken in, so that the overlying debris 

 is caving down into it. In places the tunnel is deserted by the stream, and the 

 accumulating debris thus forms a tortuous ridge, with projecting knolls where 

 the tunnels are oldest and largest. At the same time the ice on the sides at 

 some distance from the tunnel, where the superficial debris was thinner, has melted 

 down much below the level of that which was protected by the thicker deposit ; 

 and so the debris is sliding down the sides as well as into the tunnel through the 

 centre. Thus three ridges, approximately parallel, are simultaneously forming, 

 one in the middle of the tunnel, and one on each side. When the ice has fully 

 melted away, this debris will present all the complication of interlacing ridges, 

 with numerous kettle-holes and knobs characterising the kames ; and these will be 

 approximately parallel with the line of glacial motion." Again (p. 300) : — " Of 

 course these glacial streams must, in the main, have followed the great valleys ; 

 but many of the minor valleys were, at that time, so obstructed that the streams 

 might disregard them and take a more direct route over the ice through the open 

 channels and long tunnels which must have existed. Those familiar only with the 

 contracted glaciers of the Alps are scarcely prepared to appreciate the extent to 

 which currents of water flow over the larger glacial masses and rearrange and 

 transport the superficial material collected on them. The ' sub-glacial ' streams 

 also are not always strictly sub-glacial ; since they often flow through tunnels 

 which are midway between the top and the bottom of the ice-mass. In the Muir 



*Niiitli Annual Eeport Geol. Survey, ITnited States, 1887, 1888, 1889, p. 550. 

 f Geology of Minnesota, Final Eeport, vol. ii., 1888. 



