226 



Scientific Proceedings^ Royal Dublin Society. 



is almost impossible to see the third dyke unless the loose boulders covering it 

 are removed. These three dykes are of bluish-green microerystalline dolerite, 

 but the central dyke contains small white aniygdaloids slightly tinged at the 

 edges. 



The dykes pass across the little bay and reach the land, and here the 

 structure changes. The northern dyke becomes symmetrically multiple; the 

 central dyke divides, catching up three feet of shale between the parts, and 

 becomes unsymmetrically multiple. The three dykes emerge again at Oughmore, 

 and run out to sea in the direction of Aughris Head. The dykes remain 

 parallel, and their true course is shown in fig. 2, B. 



ATLANTIC 



CRCMOtE WEST 



QioaH.5 dlsblaced. to ^outtyj 

 \ 



Pollacfcorrj 



Vims. 



^^ LIMESTOWE 



.«-' 



Fig 1. 



South-east of these dykes, through a small headland similar to that mentioned 

 above, are three more dykes, which on close examination are found to be 

 exactly equivalent to the first set, though not in their course. The dykes 

 retain the same relations towards each other, and each dyke has the same 

 characteristics as its equivalent in the former set. Their course is shown in 

 fig. 2, D, and differs slightly from that marked in the Geological Survey maps 

 (fig. 2, C). 



It will be observed that the dykes do not pass through the small headland of 

 sandstones (marked shale by the Survey) at Carrickpatrick, but have been 

 displaced between the land and these rocks. The dykes run out to sea towards 

 a point a little north of Kilrusheighter sand dunes, and considerably south of the 

 point where the Pollbrean dykes would enter the land if produced. 



