THE IGNEOUS ROCKS OF THE BEREHAVEN DISTRICT. 
161 
We shall now go to the mainland, and begin, as we did on Bere 
Island, by remarking the lowest beds. Jnst at the junction of the 
Yellow Sandstone and Carboniferous slate, there is a large massive 
bed, about 80 feet thick, of green, compact felstone, traceable from 
the extreme south of the Dunboy Wood to near Pulleen Harbour. It 
is twice broken by small, white felstone dykes (about ten feet thick). 
The first you meet, going from the east, causes a downthrow of about 
200 feet; the second cuts it off, and after that it is not to be found; 
though there is a bed, which seems to have the same mineralogical 
appearances, to be found on the N. W. of Black Ball Head; but 
that lies much higher in the geological series. At Fair Head, and 
along the coasts N. E. and W., are to be found beds of felspathic 
trap, and ash and greenstone dykes. • The felstone traps are very 
well developed a little south of the last-mentioned bed, making 
their appearance as beds; but, on going more south to Fair Head, 
becoming tabular. The greenstones are mostly small. All of these 
traps are very like those on Bere Island. Going now to the west 
of Drumsharra Point—as here the Carboniferous slate is all denuded 
away to make Pulleen Harbour—we come on a large, well-developed 
igneous district, full of dykes and beds; but we find them very like 
Bere Island, felspathic near the Yellow Sandstone, and, as you go 
higher in the series, becoming more or less hornblendic, being some¬ 
times conformable and unconformable, as shown by sections, like 
those before mentioned when speaking of Bere Island,-—the whole of 
it cut up in some places by greenstone dykes. We shall leave it, and 
go west to Black Ball and White Ball Heads. On the N. W. of 
Black Ball Head there is a large, irregular mass of trappean breccia, 
a greenish-brown, earthy base, with partially rounded crystals of 
hornblende, often two inches across, and veins of asbestos; outside 
this, a breccia of fragments of trap, slate, grits, primary limestone, 
and other kinds of rock. On White Ball Head there are to be 
found four dykes of breccia, very like that first mentioned, running 
in a N. W. direction, bearing direct for the breccia, before spoken of 
among the Yellow Sandstone traps, which breccia is very like the 
outer breccia on Black Ball Head. The breccia on Black Ball 
Head would appear to have been the vent of eruption of a sub¬ 
marine volcano, and the dykes on White Ball Head, and the mass 
on the mainland, part of the funnel thereof. The Black Ball 
breccia appears to have been contemporaneous with the mass of 
Vol. VII. R 
