596 Scientific Proceedings, Royal Dublin Society. 



ROSCOMMON. 



To the north and south-west of Lough Allen are Coal-measures — 

 a small portion of the Connaught Coal-field. To the southward 

 of these, extending from the north-west margin of the county 

 eastward, past. Lough Key nearly to the Shannon, are Silurians 

 of the " Old Bed Sandstone" type, which are margined southward 

 and eastward by Lower Carboniferous Sandstones. To the west of 

 the county, both north-east and west of Castlerea, and farther 

 south-west in Slieve-Dart, are patches of similar rocks, as also 

 south-west of Roscommon ; while to the north-east of the same 

 town, in a south-west and north-east direction, is Slieve-Baun, 

 near which small exposures of Ordovicians are margined by Lower 

 Carboniferous Sandstone. 



The Ordovician grits, which are of small dimensions,- are more 

 or less inaccessible, and are very little used, even locally. 



Silurian. — These occur in the Curlew Mountains. Of these 

 there is a great thickness, and some of them are fair working 

 stones ; but in general they are hard, gritty, and of bad working 

 quality and colour. They are not in request, as limestone is pre- 

 ferred ; and if sandstone is required, those belonging to the Lower 

 Carboniferous Sandstone are used. 



Associated with these sandstones are f elspathic tuffs. Although 

 these are more of the nature of argillaceous than arenaceous rocks, 

 they ought here to be mentioned, as in places the one graduates 

 into the other. Some seem as if they would cut well; but as 

 they are in general in somewhat inaccessible or inconvenient places, 

 they have only been used for farm purposes. 



Lower Carboniferous Sandstone. — In the different exposures 

 of these rocks there are stones of more or less note. At Tarmon, 

 near Boyle, there is a bluish-grey stone, hard and compact ; but, 

 on account of the numerous joints, it is incapable of being raised 

 in large lengths. The strata varies from 10 to 24 inches in thick- 

 ness ; it has been used in many of the buildings in Boyle, but is 

 more suitable for rubble than cut-stone purposes. 



St. John's Sole. An historical quarry. — This lies north of the 

 river near Boyle. Greyish ; good, but hard ; has-been used ex- 

 tensively in Boyle and the neighbourhood, as in the bridge and 



