272 STEATIGEAPHICAL GEOLOGY 



Leitrim and Sligo. In the counties of Derry and Tyrone a series 

 similar to that of Arran and Ayrshire is found ; the basement beds 

 of red sandstone and conglomerate resting directly either on the 

 Archaean schists or on the Lower Old Red Sandstone. The Tuedian 

 or Calciferous sandstone is represented by about 2000 feet of 

 strata, about half of which consists of reddish-brown sandstones, 

 succeeded by calciferous sandstones and bands of shale which are 

 well exposed in the valley of the Moyola Eiver near Drapersdown. 

 In these higher beds the commonest fossils are, Leperditia Okeni, 

 Modiola Macadami, and Protoschizodus axiniformis, with 

 Dithyrocaris Colei, Cypris burdigalensis, and remains of fish. 



Above these beds, at Cullion and Desertmartin, limestones come 

 in which are arenaceous in the lower beds and dolomitic in the 

 higher ; the prevalent fossils are corals (Litliostrotion junceum, L. 

 affinis) and Brachiopods (Productus giganteus and Orthis resupinata). 



Southwards the lowest beds appear to thin out, while higher 

 beds come in above, so that in Fermanagh, Leitrim, and Sligo there 

 is a more complete succession which, according to Messrs. Hiill and ' 

 Hardman, is as follows : - 12 



Feet. 

 Black shales with some sandstones (Pendleside Beds) 600 



Grey limestones with nodules of chert 

 Carbonaceous shales and sandstones (Calp) 

 Lower limestones, grey and dark blue . 

 Yellow sandstones and grey shales 

 Brown sandstones and conglomerates 



500 

 1000 

 600 

 200 

 500 



3400 



The basal beds are sometimes called Upper Old Red Sandstone, 

 but they rest unconformably upon the Lower Old Red (see p. 237), 

 and are now generally regarded as Lower Carboniferous because 

 they seem to be the equivalents of similar beds in Derry and of the 

 Lower Tuedian of Berwick. 



Westward, in Sligo and Mayo, there is a similar succession, but 

 the basal beds are absent and the lower limestones pass laterally 

 into beds of calcareous breccia and conglomerate, indicating a 

 shore-line. The upper limestone rises into hills with bold craggy 

 escarpments, while the softer beds of the Calp have been eroded 

 into broad vales. 



Great Central Plain. The central part of Ireland, from the 

 shores of Dublin and Meath to Galway Bay and Lough Corrib, is a 

 great tract of low undulating land which seldom rises to more than 

 300 feet above the sea. In consequence of this low elevation, the 

 general horizontality of the limestones below it, and the prevalence 

 of Pleistocene deposits, exposures are few in the central area, and 



