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



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ridge. For suppose the esker to have had originally a rectangular section, and to 

 have acquired its existing form by the sliding down of materials, along its 

 sides, then if the base of the rectangle is greater than the altitude, in any ratio 

 greater than 3 to 2, the final height of the esker, after sliding, will be the same as 

 the original heighj; ; but if the ratio be less than this, the final height will be less 

 than the original height ; thus in one and the same esker-ridge we should expect 

 to find the broader portions higher than the narrower. 



An attempt is then made to show that the variation in height is connected with 

 changes in direction of the esker, and with associated changes in the width of the 

 meandering ice channel in which it was formed. The author admits, however, 

 that "many eskers do not display a consistent and regular variation in their 

 lines." 



In the abstract of my Paper,* on A map of the Esker Systems of Ireland, it is 

 said that the esker may represent a " cast," as it were, of a glacier-tunnel in gravel 

 and sand. On this hypothesis, all the known characters of eskers find an explana- 

 tion, as well as many incidental details, such as the long lakelets, or shallow streams, 

 by which they are not infrequently flanked. The details of the explanation are not 

 given ; but this defect is supplied by Mr. Woodworth, who, to my great satisfaction, 

 has arrived at a view precisely similar to my own. I reproduce the diagram which 



Fig. 1. (From Mr. Wood-worth's Paper just referred to.) 

 Generalized section across meridional valley, -with lateral moraine terraces (or hillside kames), with medial esker, showing 

 symmetry due to deposition of sands and gravels in the presence of melting valley-tongues of the ice-sheet. AA, ice- 

 sheet previous to the stage BB, when isolated blocks hold open cavities between the esker and the terraces, EE. C is the 

 tunnel in AA in which the esker originates. DD, esker ponds or swamps. 



he gives in illustration of this view. Dr. Hummel's explanation of the esker- 

 moat has been given previously {v. antea, p. 791). On reviewing the preceding 

 account — which is far from complete — it will be seen that ever since Hummel first 

 attributed the peculiar features of eskers to the influence of once existing ice, 

 geologists, familiar with these features, have, with almost one accord, expressed 

 themselves in agreement with this explanation. Nor could it well have been other- 

 wise. Some material must have existed to furnish a support to the sides of the 

 eskers, during theii- formation ; but this material has since completely disappeared ; 

 and the only substance at all likely to have behaved in this manner is ice. 



*Eep. Brit. Ass. Adv. Sci., p. 777, 1893. 



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