On the Physical Geology of the Neighbourhood of Dublin. 135 



sections all the way from Casana Rock, on the E., to a little be- 

 yond Drumleck Point on the S.; 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, &c, viz., the Cambrian, since Old- 

 haraia 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 — Quarts-rock and Slate near Howth, immediately east of the Needle Rocks. 



Drawn to scale (8 yards to an inch) by the late Mr. John Kelly. 



Bray Head. — The precipitous sea-side of Bray Head presents 

 for a length of nearly two miles, a fine continuous section of the 

 Cambrian Rocks, which here are greenish, reddish, and purplish, 

 grits and slates, with bands of quartz-rock. The beds have a 

 general dip to N.N.W., or ISL, at from 40 Q - to 70 Q . Allowing for 

 contortions and faults- there must be a thickness of nearly one 

 mile of the formation exposed here. Several thick bands of 



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