122 SWANSTON — SILURIAN ROCKS OF Co. DOWN. 



vad, &c, are the representatives of the Glenkiln Shales, the equivalents 

 of the Upper Llandeilo of Wales. 



2nd. The black shales at Carnalea, and the barren mudstones at Coalpit Bay, 

 represent respectively the Lower and Upper Hartfell Series, the equiva- 

 lents of the Bala or Caradoc. 



3rd The black shales of Coalpit Bay, characterised by the zones of D. acum- 

 minatus, D. vesiculosus, M. gregarius, and D. cometa, represent in part 

 both the Lower and Upper Birkhill shales, which are paralleled with 

 the Lower Llandoveries. 



4th The grits and conglomerates which immediately succeed the latter are of 

 the same age as the Gala Series, and occupy a high place in the Middle 

 Silurians. 



5th. The black shales and associated flags at Tieveshilly, near Portaferry, oc- 

 cupy either the extreme top of the Middle, or the base of the Upper 

 Silurians, and are the highest Silurians yet recognized in the North-east 

 of Ireland. 



The geographical relation of the area under consideration to that of South 

 Scotland and the general direction of the strike of the rocks in both districts, 

 would naturally lead to the expectation of a certain degree of similarity between 

 their geological characters ; from the foregoing, however, it is clear that not 

 only generally, but in detail, do they correspond in a remarkable degree. While 

 it would, perhaps, be impossible, owing to the imperfect manner in which the 

 fossil bands are exposed, to unravel the sequence of the various beds in County 

 Down from an examination of them alone, the key afforded by the recent re- 

 searches in the Scottish beds has made the subject a matter of ease. We are 

 thus enabled for the first time, with some amount of certainty, to arrive at 

 conclusions regarding the physical geology of the district. The three grapto- 

 litic shale bands and their associated mudstones have been overlaid by the grits 

 and conglomerates so conspicuous in the county ; all were folded into vast 

 waves, the crests of which ran in a direction from about north-east to south- 

 west. Subsequent denudation completely altered the contour of the district ; 

 and judging from the remnants of Carboniferous strata at Castle Espie and Cultra, 

 it seems to have been covered by rocks of that age, and to have been again 

 upheaved and subjected to denuding agencies, which probably left it in almost 

 its present state. The granitic protrusions of the Mourne and Ballynahinch 

 Mountains are supposed to have taken place during the Carboniferous epoch, 



