﻿432 DE. C. A. ilATLEY ON THE [-^-Ug. I908, 



as those forming the great bulk of the inclusions in the Lane and 

 Eush Conglomerates.^ 



It will be convenient now to discuss the stratigraphical relation- 

 ship of the Lane Limestones to the Bihunojyhyllum-JjijRestones, 

 against which they are thrown by the angular fault already 

 mentioned (p. 429). The fault-line has a sharp bend of 110° in 

 its course ; it runs from high- water mark seawards, at first in a 

 north-easterly direction, but before reaching low-water mark it 

 bends round sharply in an easterly direction across the seawesd- 

 covered rocks. A second fault splitting off this eastern branch in 

 a south-easterly direction brings in a mass of Lane Conglomerate, 

 which thus lies between Lane Limestone on the north and 

 Dibuno2yhyUum-LiTOLestone5 on the south. A continuation of the 

 north-easterly branch in its original direction produces a fault of 

 small throw, effecting a slight displacement in the Lane Limestone. 

 Still another fault strikes off the main fault ; it skirts the low cliff 

 of Drift just above high-water mark, and, running in a north- 

 north-westerly direction, throws down the Lane Conglomerate on 

 the west against the underlying Lane Limestone. 



From the curvature of the beds along the eastern branch of the 

 main fault, it seems probable that the downthrow of the beds is 

 to the south. North of the fault there is a continuous sequence 

 of about 440 feet of beds, none of which correspond with the 

 Bibunojphyllum-Limestones immediately south of this fault, except 

 perhaps the dolomitic limestones forming the core of the anticline. 

 If, as supposed, the downthrow is to the south, then the fault has 

 a throw of at least 500 feet. Apart from the stratigraphical 

 evidence, the importance o£ the fault-line is shown by the marked 

 difference in the fauna of the beds on the opposite side of the fault. 

 The beds on the south contain Dihunophyllum Muirheadi in some 

 abundance, and an assemblage of brachiopods corresponding precisely 

 with those obtained from the Curkeen-Hill Limestone (see p. 437); 

 while on the north side of the fault these forms are replaced by 

 Zaphrentis^ Densipliyllum, and Chonetes cf . comoides, none of which 

 are found on the south side. 



The question of the horizon of these beds is discussed in the 

 Geological-Survey Memoir,^ and although all the beds north of 

 the Copper-Mine Fault are designated ' Lower Limestone ' on the 

 1-inch map (Sheet 112) in accordance with the views of G. Y. 

 Du ]N"oyer, J. Beete Jukes expressed the opinion that 



* it is more reasonable to suppose that there is no true Lower Limestone any- 

 where north of Rush, but that all the beds belong to the upper part of the 

 series, or the part not very far below the Coal-Measures, whatever may be 

 their lithological characters.' 



^ At the southern end of Shenick's Island is a coarse conglomerate lying 

 unconformably upon the grits and andesites. etc. It differs in appearance 

 from the Lane Conglomerate, only in the fact that its matrix is reddish in 

 colom\ In the Geological-Survey Memoir and the Survey 1-inch map this 

 deposit is regarded as the supposed base of the Old Red Sandstone ; but it 

 differs markedly in aspect from the Old Red Conglomerates exposed close to 

 the railway near Donabate. In my opinion it is more probably a local beach- 

 rock of Carboniferous age, and on, or not far from, the horizon of the Lane 

 Conglomerate. ^ Expl. Sheets 102 & 112, 2nd ed. (1875) pp. 65-66. 



