ON THE ORIGIN OF “THE SCALP,” 
A REMARKABLE CLEFT IN THE GRANITE HILLS SOUTH OF DUBLIN. 
BY 
EDWARD HULL, s.a., F.r.s. 
Director of the Geological Survey of Ireland. 
[Read March 19th, 1877.] 
OnE of the most peculiar natural features of the neighbourhood 
of Dublin is the deep cleft, known as “'The Scalp,” by which the 
traveller is introduced into the mountainous district of Dublin 
and Wicklow, from the plain to the northward. This cleft 
traverses transversely a low spur of the ridge of granitic and 
schistose rocks which stretches from the coast of Killiney, by the 
Three Rock Mountain, Glendoo Mountain, and the ridge dividing 
the sources of the Glencree and Dodder Rivers, to Kippure, at an 
elevation of 2,475 feet.* It is in fact aravine of about 325 feet in 
depth, and at an elevation above the sea of about 500 feet along its 
bottom, bounded by steep, sometimes precipitous, banks of granite 
towards the north, and schist at the southern extremity. In this 
direction the schist is admirably exhibited in the western face of 
the hill resting on the granite; and the boundary between the two 
rocks passes across the valley without any break or displacement 
of the beds, which dip 8.8.E. at about 50°. 
The ridge which is intersected by “The Scalp” forms the 
watershed between the streams which flow into the Shanganagh 
River on the north, and those which pass into the Dargle or Bray 
River on the south, so that there is scarcely any stream in the 
ravine itself. The actual watershed as you pass along the road 
which traverses “The Scalp” is reached about 200 yards north 
* The actual watershed runs along a low ridge about 200 yards to the north of the 
entrance to “The Scalp” where the road crosses it. A small streamlet, of about a foot 
across, comes down the intervening hollow between the main ridge and the lower one 
already referred to, from the west, and unites with another streamlet which issues forth 
from a pond situated in a field close to the road. The little brook thus formed, runs 
down through the Scalp, and when visited at the end of March, 1877, and after a wet 
season, was only two feet wide and four inches deep on an average throughout a distance 
of 100 yards, 
