ON THE GEOLOGY OF THE LAKE DISTRICT OF KILLARNEY. Ill 
beds; at half a mile east of Lough Duff, in the Black Vallejo the 
lower green beds are again observed, and they occupy the entire of 
the Black Valley. 
Brassil Mountain, 1888 feet in elevation, in the Black Valley, 
and to the east of Sugarloaf, presents the same geological structure 
as Sugarloaf. On the summit levels of the Knocknabreda range, 
which skirt the Black Valley on the south, a certain set of beds 
occurs, partaking of the character of the lower as well as middle sub¬ 
divisions; these may be about 350 feet in thickness. 
If we traverse south from the Black Valley, across the rocky 
range of Knocknabreda, as far as Wind-gap, on the Kenmare and 
Killarney road, the lower green beds, with a few purple slates and 
conglomeritic layers, containing jasper pebbles, are alone observed; 
but as we descend the mountains on the Kenmare side, the rocks, 
after some well-marked synclinal and anticlinal curves, dip confor¬ 
mably under the middle purple grits and slates which form the mass 
of the mountain ranges on the north of the Kenmare valley. 
From the foregoing observations, it is clear that the Black Val¬ 
ley, with its branch to Curraghmore Lake, are valleys of denuda¬ 
tion ; the boundary between the lower and middle subdivisions of 
the Old Red, as proposed by Mr. Du Noyer, forming a contour line, 
varying from 1000 to 1350 feet above the sea. 
In describing Mangerton Mountain, he remarked, that at the 
south entrance to the Devil’s Punch-bowl, there occurs a boss of 
intruded felstone trap, about 500 feet in width, from N. to S. 
On the north side, the trap is very hard and compact, of a dull, 
purplish-gray colour, and slightly porphyritic,—the crystals being 
pale, yellowish-green felspar. It has a rudely laminated structure 
on the outer surface, where it comes in contact with the purple and 
green beds of the Old Red Sandstone. In the centre of the mass, 
the felstone weathers out in small spheroidal nodules; on the south 
side the felstone becomes flaky, passing into a green and ashy-look¬ 
ing rock, which weathers out in small dimple-shaped hollows; 
throughout, this trap weathers white. 
This is the only instance of the occurrence of a trap rock in the 
district described, but in the Horse’s Glen, to the east of Mangerton, 
dykes and bosses of greenish-gray felstone are of common occurrence. 
The most remarkable protrusion of trap in the neighbourhood 
of Killarney is one first observed in the year 1855, by Mr. Fred. 
