the North East of Ireland, 205 



It may be conjectured that the coal measures underlie the green- 

 stone through the entire range of Fairhead, since the)^ again make 

 their appearance beneath it on the east side of the promontory ; but 

 the whole of its base is too much encumbered with debris to allow 

 of our ascertaining this point. On the west side, at a lower 

 level than the coal measures, we noticed a ledge of clay porphyry 

 running out to sea ; this rock is probably analogous to the por- 

 phyries of Killnadore. 



The columnar greenstone of Fairhead, and the coal measures 

 which underlie that rock in Gobb cliff, have been already de- 

 scribed*, and I have to mention but very few additional circumstances, 

 principally relating to the whin dykes which traverse that cliff; 

 of these dykes, the first in advancing from the east, is Carrick Mawr, 

 " the great crag," a name well deserved by its dimensions : it forms 

 a broad causeway, traversing the beach and terminating in a nearly 

 insulated mass of rocks rising about thirty feet ; of this mass only 

 the central line consists of the dyke itself, the sides being evidently 

 composed of portions of the strata traversed by it, but much altered 

 in their character and degree of induration by its contact. These 

 beds appear to have been chiefly derived from the slate clay of the 

 coal measures, which has become so compact as to assume the cha- 

 racter of flinty slate. In one point this rock may be seen on one 

 side of the dyke, and on the other the sandstone grit, which usually 

 accompanies the coal beds, also in a highly indurated state : its 

 colour changed from red to white, and its mass penetrated by 



* It should be noticed, that in the section all the coal measures are coloured with a 

 dark tint, though this in fact belongs only to the coal itself and to the slate clay ; the 

 thick beds of red sandstone which alternate with these strata form the predominating 

 features of the cliif. 



This system of colouring has been adopted, becouse it seemed necessary to distinguish 

 the coal measures from the red sandstone not containing coal. 



