794 SoLLAS — A Map to shotv the Distribution of Eskers in Ireland. 



otherwise the water, which finds its way down in the higher regions to the 

 bottom of the ice, will rise again to the surface at lower levels, and find its 

 way over it. 



The surface of eskers is sometimes covered with angular detritus ; this is 

 englacial drift, which was deposited in the last stages of the melting of the ice, 

 when the running water was diminishing in strength. 



Serious reasons are given for doubting the possibility of the formation of 

 eskers from bottom moraine, at least in the manner supposed by Hummel. 



As regards the kettle-holes of eskers, Nordenskiold and Levin have suggested 

 that water, streaming through the loose material of the esker, has carried away 

 the fine sand, and so caused a settling of the residual material ; thus forming a 

 kettle-hole. This is very improbable. If such a process really occurred, we 

 should expect to find at the bottom of a kettle-hole more large stones and coarser 

 gravel than in other parts of the esker ; but this is not the case. Kettle-holes are 

 original, not super-induced, features of an esker. They may be explained as 

 marking the position of islands of ice which stood up in the middle of the rivers 

 of the ice-sheet. 



A somewhat similar explanation will apply to the interruptions which so 

 frequently occur in the course of an esker, A rapid accumulation of pebbles, for 

 instance, may cause a diversion in the course of the river, so that instead of 

 flowing through a canon, it will proceed over or under the ice. 



The author gives the following summary of his conclusions : — 



1. Eskers were formed in running water. 



2. No running water has the power to lift the contents of an esker to the con- 

 siderable heights at which they so often occur. 



3. The material must, therefore, have been lifted up by the ice, and from it 

 carried down and heaped together in the eskers, somewhat after the fashion 

 described above. 



In the discussion following the reading of Dr. Hoist's Paper, Nordenskiold, 

 Torell, and Tornebohm, took part; and it was pointed out that neither Hummel's 

 nor Hoist's theories accounted for all the peculiar features of an esker. Norden- 

 skiold called attention to the manner in which the great sand plains of North Asia 

 are being denuded, as suggesting a possible explanation of the mode of formation 

 of some eskers. 



The first geologist in America to propound a general glacial theory of eskers 

 was Warren Upham,* whose work has all the interest of independent discovery ; 

 for Winchell's explanation of a particular case, in no sense a general theory, was 



* On the Origin of Karnes or Eskers, by "Warren Upham. — Proc. Amer. Assoc. Adv. Sci., 1876 

 (1877), p. 216. 



