On the Physical Geology of the Neighbourhood of Dublin. 153 



about Foxrock, and Dalkey, on the Killiney Hills, &c. It is 

 often strikingly displayed on limestone freshly bared for quarry- 

 ing; though, of course, almost immediately removed. There was 

 a very fine example of this in a quarry near Finglas Bridge (the 

 one in which the beds are nearly horizontal). The abrading 

 agent has frequently produced very observable crag-rounding, as 

 distinct from mere surface-rounding, though generally accom- 

 panied thereby, as on Ireland's Eye, Shankill, and Bray Head. 

 This phenomenon should be viewed from a sufficient distance — 

 say from half a mile to a mile and a half — and in the afternoon, 

 when the sun is favourably situated for showing the effect, owing 

 to the direction of the glaciation. The highest point at which 

 the striations can be certainly found is on the very summit of 

 Shankill, near the Scalp, 912 feet. Unfortunately the granite 

 hills would not preserve the striations except under special 

 circumstances, otherwise those marks of ice-action would be 

 traceable to much greater heights. 



The Lower Boulder Clay is of the usual well-known character. 

 It is generally a very stiff clay containing well rubbed, blunted, 

 and scratched, though sometimes angular, and very rarely rolled, 

 stones and blocks ; these are often two feet in length, though 

 they are usually much smaller. Except in the S.E. part of this 

 district the great majority of the stones are limestone, even in 

 places situated some miles from the edge of the limestone ground. 

 As the great ice movement was from the extensive limestone 

 plain, we should naturally expect a preponderance of limestone 

 blocks in the boulder clay ; but it is sometimes very surprising 

 that the boulder clay, after having been swept along over two or 

 three miles of granite ground, should have picked up so few 

 granite blocks as it has done. In such cases the largest blocks 

 in the clay belong to the local rock. The upper surfaces of such 

 blocks are sometimes ground, smoothed, and scored in the same 

 manner as the surface of the living rock, and in the same 

 direction. 



In the N. and N.W. neighbourhood of Dublin the boulder 

 clay has been left in more or less well-defined ridges, which are 

 quite distinct from the eskers to be mentioned presently, and 

 which we shall call drumlins ; these are not only parallel with 

 each other but also with the rock-striation of their immediate 



