﻿Yol. 64.] CAKBONIFEEOTJS ROCKS AT LOUGHSHINNT. 433 



He also argues that the Hush and Lane Conglomerates are 

 contemporaneous, on the ground that the fact of a 



* conglomerate of Silurian pebbles occurring in the Carboniferous Limestone 

 would seem to be stronger lithological evidence in favour of the beds wherever 

 those conglomerates occur, being on the same geological horizon, than any- 

 mere differences in the colour or texture of the limestone associated with 

 them could be against it.' 



In the absence of direct stratigraphical evidence, the settlement 

 of these two points — that is to say, the age of these beds and the 

 contemporaneity of the two conglomerates — must be left to palaeon- 

 tological methods. As regards the former. Dr. Yaughan considers, 

 from an examination of the fauna of the Lane and Holmpatrick 

 Limestones, that both limestones lie in the Dibunophy Hum-Zone, 

 but below the CyatJiaxonia-Beds. Stratigraphical reasons already 

 given seem also to place them in a part of the zone below that 

 occupied by the Dibunojphyllum-JjiTaestorLes of the coast immediately 

 north o£ the Copper-Mine Pault. As regards the second point, 

 Dr. Yaughan, having reviewed the evidence on which he previously 

 fixed the horizon of the E,ush Conglomerate, is now satisfied 

 (see p. 442) that that Conglomerate may possibly belong to the 

 Bibimophyllum- Zone. The palseontological evidence supports 

 therefore, to some extent. Jukes's view of the correlation of 

 the two conglomerates. It is not, however, necessary to regard 

 these two deposits as being precisely of the same horizon. The 

 Rush Conglomerate-Group, with its intercalations of fine-grained 

 material and its much greater thickness, would probably require a 

 longer period for its deposition than the Lane Conglomerate ; and, 

 moreover, the physical conditions under which the Carboniferous 

 deposits of the Dublin district were laid down were such a,s to 

 make the local occurrence of conglomeratic conditions at various 

 horizons not unlikely. 



III. Sequence of Deposits in the Lotjghshinny Area. 

 [C. A. M.] 



An attempt may now be made to piece together the sequence of 

 the rocks occurring in the Loughshinny area. 



The highest beds are certainly the Loughshinny Black Shales. 

 They are underlain by the Posidojiomi/ a-Limestones, and these by 

 the Cyathaxonia-Beds of Upper Dibunophyllum-age. The Bibuno- 

 pkyllum-Ijimestones (of the age, apparently, of the Curkeen-Hill 

 Limestone) must be placed below the CyatJmxonia-Beds ; and at 

 seemingly a still lower level in the Dibunophyllum-Zone must 

 be placed the Holmpatrick Limestone, with its underlying Lane 

 Conglomerate and Lane Limestone. The beds may, therefore, be 

 tabulated as follows, the palaeontological zones being determined 

 by Dr. Yaughan : — 



F -J 



