PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 18, 



and "Western Eailway about "Woodlawn, which is the highest ground 

 it crosses*. 



This great limestone plain, which stretches, thus unbroken, across 

 the centre of Ireland, is interrupted towards the south by five chains 

 of hills, which run along bearings more or less nearly N.E. and S.W. 

 When, however, we get as far south as Waterford, Tipperary, and 

 Limerick, we meet with other ranges of hills, which run more nearly 

 due E. and W. 



Of the first five ranges of hills, two are made of Coal-measures, 

 resting conformably on the Carboniferous Limestone, and forming 

 irregular table-lands, of which the summits rise to heights of about a 

 thousand feet above the sea, and are generally near the edges of the 

 escarpments which look down in- every direction on to the low lime- 

 stone ground around them. 



The other three ranges of hills are made of Lower (or Cambro-) 

 Silurian rooks (with or without Old Eed Sandstone), rising up from 

 beneath the limestone, and attaining often to much greater elevations 

 than the Coal-measures which rest upon it. The Old Eed Sandstone, 

 where it appears, always rests quite unconformably on the denuded 

 edges of the Lower Silurian rocks, and passes up conformably into 

 the base of the Carboniferous Limestone, through a narrow band of 

 black shales. 



Of these three ranges of hills, the most eastern is the Wicklow and 

 "Wexford f range, made of Lower (or Cambro-) Silurian slates and 

 traps, with a great mass of intrusive granite, and only coated by Old 

 Eed Sandstone towards its southern termination. Its loftiest point 

 is Lugnaquilla (3039 feet), in county Wicklow. 

 , The next of the three ranges consists of the hills called Slieve 

 Bloom (1733 feet), the DevH's Bit (1583 feet), and the Keeper (2278 

 feet), and their connecting ridges. They are all composed of Lower 

 Silurian rocks, with an unconformable envelope of Old Eed Sand- 

 stone round their base, patches of the same rock being sometimes 

 left on the summits of the hills. 



The third range may be said to be formed of the Slieve Aughta 

 (1243 feet), the SHeve Bemagh (1746 feet), and the Slieve Arra 

 (1517 feet), which are of precisely similar constitution with the lulls 

 of the second range. Slieve Arra, indeed, is only separated from the 

 Keeper group by a narrow limestone valley, not so wide, in fact, as 

 the one which intervenes between SHeve Bemagh and Slieve Aughta. 



Of the two groups of high lands which are composed of Coal-mea- 

 sures, the one lies between the Wicklow and Wexford hills on the 

 east and those of the Slieve Bloom and Devil's Bit on the west, being 

 separated from them, and entirely surrounded, by a tract of low 

 limestone ground, which spreads round them from the great plain on 

 the north. The other Coal-measure high land is that which stretches 



* I am indebted to Sir E. Griffith, Bart., for a confirmation of the correctness 

 of tlie position and altitudes of these and some of the following watersheds. 



t There is, in fact, no commonly received name for the whole of this range, — 

 a peculiarity which often makes it difficult to speak succinctly of the mountain- 

 ranges in Ireland. 



