On the Physical Geology of the Neighbourhood of Dublin. 185 
sections all the way from Casana Rock, on the E., to a little be- 
-yond Drumleck Point on the §.; most of these are only to be 
reached in a boat. Some of them, as for instance that at the 
Bailey lighthouse, are composed of basalt. Notwithstanding cer- 
tain lithological peculiarities in some of the rocks of Howth Hill, 
there can be no doubt but that they belong to the’ same forma- 
tion as those of Bray Head, &e., viz. the Cambrian, since Old- 
hania antiqua (not very well preserved) was found in them by 
Dr. J. Kinahan, at Puck’s Rocks, near the N.E. point of the 
peninsula, 
PLAN.—Quartz-rock and Slate near Howth, immediately east of the Needle Rocks. 
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Drawn to seale (8 yards.to an inch) by the late Mr. John Kelly. 
Bray Head.—The precipitous sea-side of Bray Head presents 
for a leneth of nearly two miles, a fine continuous section of the 
Cambrian Rocks, which here are greenish, reddish, and purplish, 
erits and slates, with bands of quartz-rock. The beds have a 
general dip to N.N.W., or N., at from 40° to 70°, Allowing for 
contortions and faults there must be a thickness of nearly one 
mile of the formation exposed here. Several thick WEEE of 
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