﻿Vol. 64.] THE CAEBONIFEEOUS EOCKS AT LOUGHSHINIfY. 



423 



north, until they pass (fig. 8, below) under the still higher group of 

 Black Shales without limestones which form the clifFs of part of 

 Loughshinny Bay. 



The Posidonomya-Limestones are lithologically much of the same 

 character as the Ci/atJicLvonia-Beds below, but contain a larger 

 proportion of black shales and dark argillaceous limestones. There 

 are no massive limestones in this group ; many beds of limestone, 

 however, some grey, some dark, occur up to 4 feet in thickness, 

 as well as numerous seams of chert. Posidonomya Becheri abounds 

 in many layers, usually in dark calcareous shale or black shaly 

 limestone, and Posidoniella Icevis has also been recognized. About 



Fig. 8.—-Sout7i-iuestern corner of Loughshinny Bay : junction of the 

 'Posidonomy &-Limestones luith the Loughshinny Black Shales. 



9 feet below the top bed of these limestones two sandy ripple- 

 marked surfaces occur. The strike of the ripple-marks approaches 

 a north-westerly direction, and indicates that the trend of the old 

 shore-line at this spot in Carboniferous times lay in that direction. 

 The thickness of this limestone-group, ascertained by actual 

 measurement of the individual beds, is 160 feet.^ Some 30 feet 

 may perhaps have to be added to this amount, as it is possible that 

 a fault cuts off the westerly extension of the highest massive 

 limestone of the Cyathaxonia-Beds and effects a displacement to 

 this extent. 



^ Excluding the 100 feet referred to in tlie footnote on the preceding page. 



