﻿Yol. 64.] CAEBONIFEROTJS EOCKS AT LOFGHSHINNY. 



431 



The deposit differs from the Eush Conglomerates in several 

 important respects : — 



Eusn Conglomerate-Group. 



(i) The bands of conglomerate are 

 iaterstratified with shales and sandy 



(ii) The matrix of the conglomerate- 

 bands is usually a limestone. 



(iii) Fossils are not uncommon at 

 several horizons. 



(iv) Conglomeratic conditions gra- 

 duate both into the Rush Slates below 

 and into the Limestones above. 



(v) Thickness = 500 feet. 



Lane Conglomerate. 



The conglomerate retains its coarse- 

 ness practically throughout ; the only 

 interstratification of finer material 

 observed in it was one inconstant bed 

 of pebbly sandstone. 



Except at the base of the deposit, 

 the conglomerate is wholly made up 

 of detrital material. 



Fossils are apparently absent. 



The conglomerate begins rather 

 abruptly, though there are pebbles in 

 the underlying limestone that herald 

 its incoming, and it ceases quite 

 abruptly. 



Thickness = 200 feet. 



The beds both below and above the conglomerate also differ 

 considerably in each area, those in the Rush area containing much 

 more muddy detritus than those in the Lane and Holrapatrick Beds. 

 The lithological characters do not, therefore, support strongly any 

 correlation of the beds of the two areas. 



The Holmpatrick Limestone succeeds the Lane Con- 

 glomerate abruptly ; the lower part of the first bed of the 

 limestone is filled with large Silurian fragments, but above that 

 bed no conglomeratic horizons occur. Except that some small 

 quartz-pebbles may be found in the lowest ^ beds of the limestone, 

 the next 180 feet is a clear-water deposit remarkably free from 

 land-borne detritus, there being no shale-partings between the 

 limestone-beds. The beds have a low dip, usually to the north, and 

 form a rocky shore in the townland of Holmpatrick. They are, as 

 a rule, good light-grey limestones ; but many of the beds, especially 

 the lower, are more or less strongly dolomitized here and there. 

 They are characterized by Diphyphyllum suhihicinum and Campo- 

 phyllum Miirchisoni, which are abundantly present at numerous 

 levels ; and at occasional horizons they are rich in brachiopods, 

 particularly ScJiizojohoria resupinata. About 180 feet of limestone 

 is exposed before the beds disappear beneath the sands of Skerries 

 Eay, where the coast-section of Carboniferous rocks terminates. 

 The next exposures to the north, about a mile and a quarter away, 

 are of Silurian slates and grits ; while north-east of the Holmpatrick 

 Limestone, and only 750 yards from it, are the Silurian rocks of 

 Shenick's Island, made up of grey and green grits, slates, and 

 andesites, etc.: these Silurian rocks are of precisely the same kind 



^ One of the limestone-beds just above the conglomerate is obscurely oolitic. 

 It is the only oolitic bed observed in the whole of the coast-section from 

 Rush to Skerries. 



Q.J.G.S. No. 255, 2f 



