i. 1782.4 
LXXI. 
ON THE OCCURRENCE OF ANATASE (XANTHITANE ?) 
AND BROOKITE IN THE QUARTZITES OF SHANKILL. 
By PROFESSOR J. P. O’REILLY, C.E., Royal College: 
of Science, Dublin. (Puarz XXV.) 
[Read Marcu 16, 1898; Received for Publication Marcu 18, 1898; 
Published June 11, 1898.] 
Tue outcrop of Cambrian strata, with accompanying quartzites, 
which forms the mass of Carrickgollaghan, the most northerly 
outcrop of this formation in the vicinity of Dublin, extends in a 
N.E./S.W. direction from Phrompstown in the 8.W., to quite 
near the village of Shanganagh in the N.E., and is represented on 
the Geological Survey Map No. 121 with a total length of very 
nearly two miles in the direction mentioned, and a greatest breadth 
of about 4th mile at a point lying about 4rd of the total length 
from its S.E. extremity. 
Along the south-eastern margin is shown on the map an out- 
erop of quartzite; and a mountain road runs along it, from where 
it meets the Old Connaught-road at Shankill Castle, to where the 
formation terminates in the S.W. 
The characteristics of the formation are given in the explana- 
tory memoir to the sheets 121 and 130 (1869), p. 23, wherein it 
it is stated that the country included in the two sheets is divided 
into districts of which the first (a) is the ‘“ Carrickgollaghan 
District,” which is thus described :— 
“The quartz rock of Carrickgollaghan Hill occurs in the form 
of a narrow ridge striking N.E./S.W., one mile and a-half in 
length, with a maximum width of 250 yards. At the S.W. 
extremity, where it also attains the greatest elevation of 912 feet, 
light-greenish and grey sandy slates, like Cambrian rocks, show 
themselves in the ground on the northern side, and, taken together 
with the quartz rock, would point to the Cambrian as being the 
group to which these rocks most probably belong. 
