﻿Vol. 64.] CARBONIFEROUS ROCKS AT LOUGHSHINNY. 419 



appearance of these shales is mentioned in the Geological-Survey 

 Memoir,^ where it is noted that the ends of some of the limestone- 

 beds seem to abut against them ; but the opinion there held that 

 the shales are the Upper Shales (that is, the Posidonomya-hea,ring 

 Black Shales of Loughshinnj^) introduced by faulting seems quite 

 untenable, except possibly as regards the small exposure of black 

 shale referred to as (iii) above. The only faults that occur between 

 the decomposed shales and the limestones are of insignificant 

 throw, and altogether inadequate to account for the apparent dis- 

 appearance of 250 feet of rock. 



It is very possible that the highest 50 feet of weed-covered 

 limestones, from which no fossils have been collected, may belong to 

 the Posido7io my a-Jjimestone beds that are seen on the north side 

 of the Drumanagh headland ; but the remaining 210 feet exposed 

 on the south side of this headland are proved from the stratigraphy, 

 and from the apparent absence of beds containing Posidonomya 

 Becheri, to belong to that part of the CyatJiaxonia-suhzone which 

 €omes immediately below the Posidonomy a-ljimestones. 



The prominent headland of Drumanagh projects between Roaring 

 Well Bay on the south and Loughshinny Bay on the north, and is 

 formed of an anticlinal mass of the highest beds of the Irish 

 Carboniferous-Limestone formation. The rocks on the south side 

 of the headland have just been described, and, if the coast along the 

 eastern shore be now followed, a massive bed of limestone is first 

 seen at the south-eastern corner; while, about 50 feet lower in 

 the sequence, occurs another semi-massive brecciated and cherty 

 limestone in about two beds, measuring together some 8 feet in 

 thickness (see fig. 6, p. 420, and C of fig. 3, p. 416). This mass 

 has a hummocky upper surface, due to many rounded inclusions of 

 limestone, which range up to 3 feet in length. The centre of the 

 anticline is now reached and is seen to be faulted, the fault-plane 

 being filled with breccia cemented by calcite ; but there does not 

 seem to be any serious displacement of the beds. 



The beds on the northern slopes of the anticline are well exposed 

 along the shore. They dip at first seawards, that is, in an 

 easterly direction ; but the undulating strike soon veers to the 

 west, and the dip becomes a northerly one. The beds have much 

 the same litholoj^ical character as those exposed on the southern 

 limb of the anticline. Three massive limestones occur in the sequence 

 here. The lowest is 10 feet thick ; the thickness of the second 

 is much greater, but is difficult to determine, as from the lie of the 

 fossils the limestone seems to have undergone some folding ; the 

 highest massive bed varies from 25 to 30 feet in thickness, is 

 cracked all over, and is brecciiform towards the base. The top 

 of this highest massive bed may conveniently be taken as the 

 top of the normal Cyatha.vonia-Beds, since the overlying beds, 

 though yielding the same general fauna, are found to contain in 

 addition at numerous horizons examples of Posidonomya, especially 



1 Expl. Sheets 102 & 112, Mem. Geol. Surv. Irel. 2nd ed. (1875) p. 64. 



