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11. 



THE CAEBONIFEEOUS COAST-SECTION AT MALAHIDE, 



CO. DUBLIN. 



By LOUIS B. SMYTH, B.A., "ScB., 

 Lecturer in Palseontology, University of Dublin. 



Plates I and II. 



Eeaii NovEMiiER 25, 1919. Published Febrdary 11, 1920. 



I. — Desceiption of Section.! 



The section lies about nine miles N.E. of Dublin and one mile E. of Malahide, 

 and is a little over one mile in length. It consists of limestones and shales, 

 the former being in places dolomitized.' The rocks are exposed almost 

 exclusively between tides. The general dip is northwards) The more 

 argillaceous beds show cleavage dipping at 60° towards N., 35° W. 



Three faults interrupt the sequence. Of these, the southern occurs just 

 under the Carrickhill martello tower, and will be referred to as the Carrick- 

 hill fault. The middle one is 120 yards S. of the coastguard station, and, 

 will be called the C.G. fault. The northern (N. fault) is 230 yards N. of 

 the coastguard station, and is marked by a dyke-like mass of dolomite. 



The exposure is thus divided up by the three faults into four blocks, 

 v/hich are lettered in the accompanying map E, F, G, H, respectively, from 

 N. to. S. 



The commonest type of rock is a very impure, shaly limestone, full of 

 lenticular masses of purer limestone, mostly of small size. These lenticles 

 have frequently had their original orientation altered by the pressure which 

 produced the cleavage. In such cases the bedding is only to be made out 

 when viewed from a distance, or when layers of shells are present. 



Parts of the exposure are much dolomitized, sometimes sufficiently to 

 completely destroy the fossils. This is particularly the case in the vicinity 

 of the northern fault. 



Thick beds of shale are found at the extreme northern end, and also 

 south of the Carrickhill fault. As will be seen in the sequel, the latter beds 

 belong to a horizon a little higher than the former. Elsewhere thin beds of 

 shale occur occasionally. 



1 Reference : Geol. Suryey, Ireland, 1-inoh map, sheet 102. 



SOIENT. PROC. R.D.S., VOL XVI, NO. II. 



