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



The kettle-holes, which occur between two closely adjacent eskers, are 

 probably due to the form of the bottom surface of the ice ; those, however, which 

 run down the middle of a single ridge are possibly a consequence of waterfalls 

 through the ice. The interruptions of the eskers, their variation in height, and 

 winding form, even within a well-marked valley, are all the natural result of 

 changes in the number and strength of the lateral rivers. That the windings 

 have been so well preserved may be due to the cessation of the movement of the 

 ice, shortly after their formation, as a consequence of its melting. 



The frequent deviation of eskers from the direction of the glacial striation is 

 due to the ramifications of the ice valleys ; and from these ramifications also result 

 esker spurs and knots. 



The absence of eskers from large wide valleys might be explained, in cases 

 where tbe ice was not moving with the slope of the ground, by assuming that the 

 watershed of the drainage on the ice ran along with, or across, the hollow of the 

 underlying valley. 



It is to be remarked that : — 



1. Eskers usually proceed through valleys, even when these occur on plateaus. 



2. The slope of the inland ice, if its thickness be comparatively small, is 

 dependent on the slope of the ground, and the more so as melting proceeds. 



3. Valleys in the land, particularly in high-lying tracts, exert an important 

 influence on the position, or direction, of the ice-flow, or its depressions ; tlie more 

 especially as the whole movement of the ice in the latest times followed, in general, 

 the large and regular valleys. 



That exceptions to the above rules are numerous appears from a comparison 

 of the direction of eskers and glacial striae ; and their significance is great, as by 

 them, alone, can we obtain simple explanations of such facts as the follovnng: — 



The often obvious independence of the eskers and the slope of the ground, their 

 great and numei'ous interruptions, their isolated position, the appearance they 

 often present of having been very rapidly heaped together. These facts may be 

 regarded as the effects of changes in, and on, the inland ice, and in the volume 

 and velocity of the lateral streams. 



That the ice and the subglacial rivers may have moved in contrary directions, 

 for longer or shorter distances, is clearly shown by observations on the structure 

 of some gravel deposits ; the most beautiful example occurs between Hilleshult 

 and Svensbygget (Hallandj. At the S.W. end, on the highest ground, this is 

 extremely insignificant, and consists only of pebbles; its dimensions increase 

 rapidly towards the N.E., but the material does not change until near Hilleshult ; 

 there the pebbles are fewer, the material is more water-worn, and there is more 

 sand. This change of structure, on the whole, obtains less, if at all, in the definite 



