162 
JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
slate, and there must have been an aqueous force in action at the 
time of its formation, as the mass is blended in with the surrounding 
slate, coarse near the centre, and getting finer as it recedes therefrom. 
Out of it there proceed a number of dykes, most of them felspathic, 
but a few hornblendic, which are partially intrusive at their origin; 
but they seem, at a little distance from it, to run evenly between 
the beds. At the north of White Ball Head there are two very 
crystalline greenstone dykes, which are not traceable far; also at the 
point there is a thin bed, about two feet thick, of trappean breccia 
running for about 300 yards, and then changing into a slaty grit. 
It would seem that just at this period the volcano made a slight 
movement, and that the aqueous power had spread its debris over 
the bed of the ocean. To the north of the breccia on Black Ball 
Head there is a system of dykes close together, one of which is 
very like the green compact felstone mentioned before, near Dun- 
boy. 
Under the Black Ball Tower there is a large mass of green¬ 
stone, quite different from any other of the greenstones found in 
the Carboniferous rocks of the district: in the first place it is con¬ 
temporaneous ; it lies a good deal higher in the series, being up among 
the black slate; and it is compact, very like the dykes found in 
the Old Bed at Cod Head, only that it has not the light green 
patches with asbestos in them. It seems to have been poured out 
at two distinct periods,—as at the east side there is a small bed of 
green and black slate, about nine inches wide, which runs through the 
mass under the Tower. This finishes the trap in the Berehaven 
district. 
