Yol. 65.] THE BOCKS OF THE TOTTRHAKEADY. DISTRICT. 141 



VII. Pal^iontological Appendix. 

 By F. E. Cowper Keed, M.A., F.G.S. 



A. General Remarks on the Fauna. 



(1) The Limestone (Tourmakeady Beds). — The fauna of 

 the limestone is not rich in species, but the fragmentary nature 

 of the organic remains is the main obstacle to a satisfactory know- 

 ledge of its characteristics. Members of the genus fflcenus seem to 

 be the most abundant fossils. In spite of the matrix and mode of 

 preservation of the fossils resembling those of the Chair of Kildare 

 and Keisley, the facies of the fauna must be regarded as indi- 

 cating a considerably lower horizon, for not only are the typical 

 species of the Upper Bala 1 absent, but the assemblage is not that 

 of the Middle Bala, and certain genera and representative species 

 which occur in it are only known elsewhere from beds correlated 

 with the Lower Bala (Llandeilo). Of such fossils we may especially 

 note the species of Pliomera and Porambonites. The genus 

 Pliomera occurs abroad only in the lower part of the Ordovician — 

 on horizons generally regarded as homotaxial with the Arenig and 

 Lower Bala. Such is the case in Scandinavia, the Baltic provinces 

 of Bussia, and North America, while in Scotland and Ireland it is 

 found only in the Craighead (Stinchar) Limestone and in the 

 Tramore Limestones respectively, which are believed to lie consider- 

 ably below the Middle Bala. No undoubted representative of the 

 genus from beds of later age than Lower Bala is definitely known. 

 The same remarks apply to the genus Porambonites, which is 

 especially characteristic of the lower stages of the Ordovician in the 

 Baltic region. The evidence of the other fossils from the limestone 

 is inconclusive — as either the species have a considerable vertical 

 range, or are local in distribution, or are doubtfully identified 

 owing to the poorness of the material available. 



The new species in the fauna (to be subsequently described) do 

 not afford any evidence contrary to the view above expressed, and 

 the affinities of IUcenns weaveri support it. We may therefore 

 refer the limestone to a horizon not higher than the Lower Bala, 

 but the facies is distinct from that met with in Wales in the 

 Llandeilo Limestone, and no British Ordovician limestone is known 

 with the same type of fauna. It is to the South of Ireland that 

 one must look for features of resemblance, and in the Tramore 

 Limestones of County Waterford, described by me in 1899 (Quart. 

 Journ. Geol. Soc. vol. lv, pp. 718-72), we may see consider- 

 able affinities, although the Mayo beds have a much less rich 

 and varied fauna, and lack certain characteristic forms. But the 

 presence of the rare British genera Pliomera and Porambonites 



1 The terms ' Upper, Middle, and Lower Bala ' are used here as respectively 

 equivalent to the Ashgillian, Caradoc, and Llandeilo defined by Dr. Marr in 

 his 'Principles of Stratigraphical Geology' (Cambridge, 1898) pp. 165 et seqq. 



