ON THE GEOLOGY OF THE LAKE DISTRICT OF KILLARNEY. 107 
the pebbles of jasper ranging from the lowest to the uppermost of 
the conglomeritie beds; these can be observed on the very summit 
of Purple Mountain. Descending from Purple Mountain into the 
Gap of Dunloe, by the small lake called Glass Lough, and following 
the stream which flows out of it into the Gap, the upper purple 
grits and slates are observed to dip with tolerable steadiness to the 
east, at 20° to 25°, for the distance of about a mile and a half; nor 
do we get out of these purple beds till we descend to the elevation 
of about 1000 feet, or 413 feet above the level of this portion of the 
Gap; we have, therefore, passed through a thickness of purple grits 
and slates, amounting to 1730 feet, as determined by the elevations 
given on the Ordnance Maps; but if we measure by the probable 
stratigraphical thickness, we have from 2000 to 2300 feet as the 
most probable amount. 
In the Gap of Dunloe, below the beds just described, we again 
find the greenish-gray grits, with conglomeritie layers, cornstones, 
and purple and green slates; these appear at both sides of the Gap 
with the same strike and angle of dip, viz,,-—20° to 25° E. At the 
west side of the Gap the boundary line between the lower and the 
middle beds of the Old Eed is about 250 feet higher than on the 
east, as would be the case if the beds on either side were projected 
across. Hence it is evident that the Gap of Dunloe is a valley of de¬ 
nudation, excavated along the strike of the beds. 
Proceeding north through the Gap, the lower beds continue till 
we reach the southern extremity of the Black Lake. Here, on the 
east side they are observed to move round to the N. E., having the 
upper purple beds above them, which form the needle-like pinnacles 
called Tomies Rocks; and on the west of the Lake they appear to 
be cut off by an east and west fault, which, like that at Glen a, brings 
the upper purple beds abutting against the lower greenish grits. 
All the rocks round Cushavally Lake in the Gap are lower green 
beds; and, at the fault observed to the south of the Black Lake, 
these beds have a dip to the S. S. W. at 15°, with upper purple beds 
abutting against them on the north. 
The cliffs overhanging this Lake consist of purple grits and slates, 
with a few cornstones, having a wavy dip to the west of 25°; and 
the uppermost observed beds have thick purple conglomerates, with 
cornstones through them,—the pebbles being quartz, and occasion¬ 
ally jasper. Still more to the north, beyond Coosane Lake, the road 
