82 
THE GEOLOGIST. 
word, 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 
jS^ew Red Sandstone and probably Tertiary rocks, the adjoining 
portion of the earth's crust was being gradually raised from beneath 
the sea, and wellnigh eftectually 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, 
1862, 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 Y.) 
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- 
tegration of the local sandstones, dark grey grits, and black shales 
and 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- 
boniferous 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 IGO feet above the sea. 
