SoLLAS — A Map to show the Distribution of Eskers in Ireland. 817 



eastwardly-directed ridges occur on the eastern margin of the north-westwardly- 

 directed group, lying between some of the north-westwardly-directed ridges; 

 and, similarly, some of the north-westwardly-directed ridges lie within the area 

 occupied by the north-eastwardly- directed ones. For this reason it will be 

 convenient to speak of the two groups as the Caltra chiasma, Caltra being a 

 village lying within the system. Although most of the eskers of the chiasma are 

 straight, there are a few exceptions ; two, in particular, may be mentioned ; they 

 will be seen in the middle of the north-westwardly-directed group, and are of 

 especial interest, since they only just fall short of uniting the different directions 

 of the two groups in themselves. One commences as a north-westwardly-directed 

 ridge, and curves round until it points east of north ; its neighbour on the west 

 overlaps it for the first half of its course, and continues to approach the north-east 

 direction of the second group, without, however, quite succeeding in attaining 

 actual parallelism. So that here the two groups may be said to inosculate. 



This completes our survey of the two great systems of Irish eskers. Several 

 isolated chains and ridges occur outside these systems, such as those of Eoscrea, 

 and those to the east of Lough Derg, to which we should add, on account of their 

 interest as occurring in or near Dublin, that on which Christchurch stands, and 

 the small chain of Grreenhills and Lucan. Others, but they are not numerous, are 

 to be found in parts of Ireland which lie outside the boundaries of our map. 



Summary and Conclusions. 



Our knowledge of eskers is, in many important respects, singularly incomplete ; 

 and there are many problems connected with their origin which might perhaps be 

 readily solved by an appeal to the eskers themselves. Deeply conscious of my 

 own ignorance respecting several particulars which yet may be accessible to 

 observation, I had originally intended to publish the accompanying map without 

 comment ; but having been led to add descriptive matter, and then an account of 

 the literature of the subject, I venture to complete this essay with a short summary 

 of facts and general conclusions. 



A map of an esker system (PI. lxix.) presents a remarkable resemblance to a 

 map of a river system. The narrow linear outlines, the meandering course, the 

 branches converging like tributaries, or diverging like the channels of a delta, the 

 loops and knots are singularly alike in each. 



The chief difference which distinguishes the esker chain from a river system 

 is its discontinuity, gaps of various length, from a few yards to several miles, 

 breaking it up into a number of links of unequal size. 



The explanation of this feature has been much discussed ; chiefly, it may be 

 imagined, because it is susceptible of explanation in so many different ways on 



IHAHS. EOT. DUB. SOC, N.S. VOL. V., PAEI XTTT. 5 Z 



