[Proceedings Belfast Nahiralists' Field Club— Appendix, 1876-77.] 



ON THE SILURIAN ROCKS OF THE COUNTY DOWN. 



Part I. — Correlation. 



BY WILLIAM SWANSTON, F.G.S., 



Hon. Assoc, of the Belfast Nat. Hist, and Phil. Soc. 



•>£<* 



INTRODUCTION. 



In a paper which I had the honour of reading before the Club in March, 1875, 

 I endeavoured to give some particulars of a series of fossils which I had obtained 

 from the Silurian rocks of the County Down. At that time I had succeeded in 

 procuring them from only one locality — Coalpit Bay, near Donaghadee,— and 

 the results did not exceed fifteen species. Further research in the same locality, 

 and a more extended examination of the district, have been rewarded by a large 

 addition to the list, affording better evidence than has hitherto been available 

 for determining the geological position of the rocks in which they are found. 



The .Silurian rocks of County Down form part of an area which is rudely 

 triangular in form. A line drawn from Grey Point on the shore of Belfast 

 Lough in a south-westerly direction through Holywood, along the valley of the 

 Lagan, by Lisburn and Waringstown, would mark its north-western boundary. 

 The Irish Sea bounds it on the east, and to the south the Carboniferous lime- 

 stone forms the base of the figure by an irregular line running westward from 

 Drogheda. It comprises the greater parts of the Counties of Down, Armagh, 

 Monaghan, Louth, Meath, and Cavan. The district is an agricultural one, 

 its surface of an undulating or hillocky character, possessing few elevations 

 deserving the title of mountains, the granitic areas of Mourne, Carlingford, 

 and Ballynahinch being excepted. It is not intended in the present paper to 

 G 



