Swanston— Silurian Rocks of Co. Down. 123 



they are certainly subsequent to the deposition of the Silurians, which have 

 been forced up and highly metamorphosed by them. The north-western 

 boundary of the Silurian area has been subjected to the greatest amount of 

 upheaval, and as denudation has reduced all to a somewhat uniform elevation, 

 the lowest beds are here consequently most exposed. The Ballygrot beds form 

 the axis of what was the most north-westerly anticlinal, the black shales of 

 Crawfordsburn, Carnalea, and Orlock Point possibly represent waves of minor 

 importance ; while that at Coalpit Bay seems to have been one of considerable 

 elevation. 



Southward of this no exposures of the underlying shales are seen in Down ; 

 on the contrary, they and the overlying grits and conglomerates sink into a 

 trough and are covered by higher beds at Portaferry in which the dark 

 fossiliferous shales of Tieveshilly occur. Still further south, near Ardee, in 

 County Louth, the underlying beds again come to the surface, the black 

 Graptolite shales of the Hartfell series being well represented, in association 

 with arenaceous bands containing other fossils of Bala or Caradoc age. 



The foregoing exposition of the Silurian rocks of the County Down has 

 been very much facilitated by the aid so kindly afforded by Charles Lapworth, 

 Esq., F.G.S., of St. Andrews, who undertook the revision of the Graptolithina 

 of our rocks ; to his acuteness and critical judgment it is owing that our list 

 of species is so extensive, many of the forms would otherwise have escaped 

 detection. The monograph, with figures of the Graptolites of the County Down, 

 which accompanies this paper is the most complete hitherto published in 

 Britain, and I cheerfully acknowledge the obligations under which Irish 

 geologists are placed for this synopsis of a most difficult group of fossils. 



Through the kindness of William Bullock, Esq., of Donaghadee, I have 

 had access to the fine collection of Coalpit Bay fossils, made by his father 

 the late William Bullock, Esq. In addition to enriching my collection with a 

 number of good specimens, Mr. Bullock has also placed a valuable series 

 from the above locality in the Belfast Museum. The set has been completed, 

 as far as possible, by a selection from my own collection, embracing forms 

 representing the various beds, and including several type specimens, all of 

 which will be available for future reference. 





