O’Rettty— Anatase and Brookite in Quartzites of Shankill. 738 
“Blue and black slates are seen on its southern side, the 
discerned dips on the latter being to the southward at 30°. A 
bed of greenish felspathic ash occurs in the black slates at the 
southern boundary of the quartz rock, which fact, together with 
their colour and character, would group them in the Lower Silurian, 
rather than with the Cambrian rocks of the district. At the 
distance of 250 yards N.W. of the summit of Carrickgollaghan, 
there occurs a thin band of grey quartz rock about + mile long 
and 40 yards wide, having smooth greenish-grey slates at either 
_ side of it. This and the former quartz band appear to belong to 
a boss of Cambrian rock, which probably rises through the dark 
Silurian slates and schists.” 
At p. 14, in the general description of the ground, it is stated :— 
** At Carrickgollaghan, a boss of Cambrian slates and quartz 
rock appear through the Silurian rocks within half a mile of the 
surface edge of the granite. This is the closest surface approxima- 
tion of the Cambrian to the granite, the width of the Silurian band 
being elsewhere never less than two miles, one half of which is 
metamorphosed into mica schist.” 
It is further added :— 
“The relations of the Silurian to the Cambrian are everywhere 
very obscure, and to the north of Roundwood are absolutely un- 
determinable.” 
At p. 9, under the heading “ Formations or Rock Groups 
entering into the Structure of the District,” is mentioned “quartzite 
or quartz rock.” Of this rock it is stated :— 
“Here and there throughout the Cambrian rocks, there occur 
great belts and groups of beds of quartz rock. This has generally 
some shade of brown or yellow, sometimes becoming reddish, 
sometimes almost white; when examined with a lens, it is seen to 
be made up of minute granules of quartz, bound together by a 
siliceous cement, into a smooth, almost compact stone, intensely 
hard, but rather brittle.” 
At p. 10 is the statement :— 
“Tt is jointed in every direction both by large visible joints 
and smaller imperceptible ones, which cause it to break up into 
small angular fragments. The original bedding of the rock can 
hardly be discerned in it, and its stratification can only be de- 
termined by following its upper and under surfaces, and tracing 
