98 



Proceedings of tJte Rot/al Irkh Academi/. 



over to Mr. Fearnsides, who, from this and all other available 

 information, together with his field-notes, has written the present 

 paper. 



The Pomeroy district of Central Tyrone lies on the south-east 

 border of the Derry and Donegal Highlands, and adjoins the lowest 

 pass between the waters of the Eann and the Foyle, Blackwater, or 

 Shrule, over which the railway from Portadown to Omagh passes. 



As a district of geological interest, the Pomeroy or Desertcreat 

 district, as it was then called, was first recognized by Patrick Doran 

 and other official collectors sent out during the Ordnance Survey of 

 1838, and as a district of known Silurian rocks remains uncoloured 

 on Griffith's geological map of Ireland of 1839. In 1845 Desertcreat 

 was made known to geologists by the publication of Portlock's 

 "Geology of the County of Londonderry, and parts of Tyrone and 

 Permanagh." In that great work, Portlock shows that, from his 

 examination of the fossils, he is able to identify the Caradoc sandstone 

 division of Murchison's "Silurian System," and appends an accurate 

 monograph and description of some 216 species of fossils obtained 

 therefrom. 



The Report also includes a description of the lithology of the rocks 

 discussed, and a map upon which all available localities are carefully 

 plotted. 



For the purposes of the new one -inch Geological Survey map, the 

 district was re-mapped by Joseph jS'olan in 1877, and the sheet memoir 

 published in 1878 ; the dips and exposures of strata indicated by 

 Portlock were more accurately replotted on this map, and the memoir 

 contains a comprehensive list of the fossils of the district, compiled by 

 W. H. Bailey. 



The Graptolites originally described by Portlock are referred to in 

 several papers on Irish Graptolites by Lapworth ;^ but although 

 this author then pointed out that those Graptolites cannot belong to 

 Bala or Caradocian rocks, it was not until the appearance in 1895 of 

 the brief note in Watts and Mc Henry's " Catalogue of the Rocks 

 and Fossils in the collection of the Geological Survey of Ireland," 

 which refers them to the Llandovery or Tarannon, that they came to 

 be regarded as belonging to a series other than that which contains 

 the Desertcreat Trilobites. 



In 1885 Marr and Roberts, for the purposes of the identification of 



^ Pioc. Belfast Nat. Field Club, 1877, Appendix. Ann. Mag. Nut. Hist. (5), 

 vol. iii., 1879-1880. 



