fx 



»&. 



[Proceedings Belfast Neutralists' Field Club— Appendix ; 1876-77.] 



ON 



THE GRAPTOLITES OF COUNTY DOWN, 



By CHARLES LAPWORTH, F.G.S. 



The Graptolites discovered by Mr. Swanston in the black carbonaceous shales 

 among the Silurian rocks of County Down constitute a very distinct assemblage, 

 which is identical with that afforded by the Graptolitic bands forming the well- 

 known Moffat Series of the south of Scotland. In Scotland the containing 

 deposits have already furnished sufficient stratigraphical and palaeontological 

 evidences to allow of the determination of their natural divisions and subdivi- 

 sions, and of their precise systematic position in the general succession of Silu- 

 rian deposits. The black shales of County Down, however, are so excessively 

 convoluted and shattered, that as yet it has not been found possible to fix either 

 their total thickness or the characteristics of their component zones. That the 

 general grouping of the beds among them is essentially similar to, if not iden- 

 tical with that of the Moffat Series, may nevertheless be regarded as certain. 

 Exactly as in South Scotland, certain special forms are invariably found in 

 association, while the proportion of the species, and the lithological features of 

 the containing beds, are absolutely identical with those of the corresponding 

 zones of the Moffat Series. It is possible that in the future, local stratigraphi- 

 cal testimony respecting the inter-relations of the various beds may be detected ; 

 but the sequence of the different fossil groups in the South of Scotland is so 

 clear, that beyond demonstrating their identity with those of the Moffat Rocks, 

 this would add but little to our present knowledge. 



The Coalpit Bay Division of the County Down Silurians has yielded all 

 the Graptolites of the Birkhill shales, with the exception of one special group, viz., 

 that of the Rastrites maximus zone, which lies at the very summit of the Moffat 



