OF THE NORTH 0¥ IRELAND. 533 



shales, and quartzose calcareous pebbly beds; higher up are hard 

 green grits and bluish shales, remarkable quartz pebble-beds highly 

 calcareous, dark shales full of remains of Modiola MacAdami *, and 

 thin arenaceous limestones, the surfaces of which are curiously 

 cut up with cross systems of joints, apparently due to rapid desicca- 

 tion. Higher up no rocks are met with for a quarter of a mile, 

 where what seem to be the same series reappear and continue to the 

 boundary of the metamorphic rocks, from which they are separated 

 by a fault. In the district to the east, however, there is sufficient 

 evidence that they underlie the Lower Limestone. 



All these rocks are cut up by numerous small faults, which, 

 indeed, seem characteristic of this series, being also observed at 

 Altmover Glen, Dungiven, and wherever similar rocks are exposed. 

 Most of the sections in this neighbourhood have been described with 

 considerable minuteness by General Portlock, in his Geological 

 Eeport on Londonderry, &c. 



In most localities there is a prevalence of soft yellow sandstone 

 and sandy shale with calcareous sandstones and impure limestones, 

 often magnesian, chiefly near the junction with the underlying con- 

 glomerates. Possils, though rare, were found in several places, as at 

 the Hass, Dungiven, where there are plant-remains and also scales 

 of Holoptychius PortlocJci, Ag., and at another locality one and a 

 half mile N.E. of this, where fragments of Calamites were found. 

 In Altmover Glen similar plants occur, with others which Portlock 

 doubtfully refers to Pecopteris ; here also are shells which he 

 believes to be Producti. There is therefore no doubt that this 

 series of sandstones &c. should be classed with the Carboniferous 

 system ; and I think the whole facts of the case show that they 

 should be considered the representatives in time of the Coom- 

 hola grits and Carboniferous slate of the south of Ireland, and the 

 Calciferous Sandstone of Scotland, which Jukes regarded as the 

 equivalent of these formations. The following table shows the 

 correlation of these rocks with those in the south of Ireland and in 

 Scotland : — 



North of Ireland. South of Ireland. Scotland. 



5. Lower Limestone. Lower Limestone. Lower Limestone. 



4. Yellow, white, red, and ^ 



grey sandstone, often 



calcareous, in some 



places pebbly, wi,th 



thin bands of impure 



limestone or dolomite 



and dark shales with 



ModiolcB &c. (White 



Water and Dungiven 



beds.) 



* Portlock also found the following fossils in these beds : — Posidonomya 

 complanata (locally abundant), Dithyrocaris Colei, B, orbicularis, Cephalaspis ? 

 (fragmantof). 



Carboniferous slate and Calciferous Sandstone 

 Ooomhola grits. series. 



