82 



THE GEOLOGIST. 



word, u Denudation" In truth, there is no reason why, at one 

 period of our geological history, the great mass of the bituminous 

 coal-bearing strata occurring in England should not have extended 

 over what is now Ireland ; but, strange to say, while this store of in- 

 estimable wealth was being preserved in England, and covered by the 

 New Eed Sandstone and probably Tertiary rocks, the adjoining 

 portion of the earth's crust was being gradually raised from beneath 

 the sea, and wellnigh effectually denuded of its carbonaceous cover- 

 ing. Ireland, therefore, for the most part, presents an older geolo- 

 gical surface than England, especially over the areas now occupied by 

 the Devonian and Carboniferous rocks ; and I believe that all we 

 have now remaining to us in the upper portion of the latter, is some 

 of the basal beds of the English coal-measures., represented by three 

 thin layers of bituminous coal, capping the mountains at either side 

 of Lough Allen, in the counties of Roscommon and Leitrim, and 

 extending into the Co. Sligo. 



The most important coal-beds of the Arigna district, or those 

 which are being worked at present, occur to the west of Lough 

 Allen, and near the summits of the mountains of Kilronan and Alta- 

 gowlan ; the former being 1081 feet, and the latter 1377 feet above the 

 sea, having the valley of the Arigna river between them.* Erom an 

 examination of these coal-fields, which I made in the month of March, 

 18(52, 1 am enabled to add some information to that which we already 

 possess regarding them, which, I have no doubt, will be acceptable 

 to those who are interested in the subject of the Irish bituminous 

 coals. 



The accompanying view of these mountains, taken from a boss of 

 carboniferous limestone on the roadside near Drumshambo, on the 

 way to the old Arigna iron-works, may convey some idea of the 

 general aspect of the country. (See Plate V.) 



The flat middle distance is occupied by the carboniferous lime- 

 stone, the low ridge beyond, which rests on the S.E. flank of Kil- 

 ronan Mount, is formed entirely of drift, derived from the disin- 

 herit ion of the local sandstones, dark grey grits, and black shales 

 ami ironstones of the coal-measures. The Arigna river passes through 

 the gap in this ridge ; to the extreme left of the view a boss of car- 

 bon iferous limestone makes a feature in the landscape, and the slope 

 of the hill above it, which is deeply intersected by small stream- 

 courses, is composed of the black ironstone shales and dark grey 



* The level of Lough Allen is 160 feet above the sea. 



