378 Proceedings of the Royal Irish Academy. 



igneous rocks were folded and sheared out together before the disposi- 

 tion of the Old Eed Sandstone, as is shown by the contained stones of 

 the former in the latter. 



Throughout Donegal, Tyrone, and Londonderry similar conditions 

 and varieties of rocks are found to exist, namely, a lower pebbly grit 

 series, with their black shale or schist beds, probably of Llandeilo age, 

 then a passage upwards into black shales or slates greatly deformed 

 by movement, and sometimes pyritous, above them the limestone 

 zone, probably of Bala age. On top of the limestone that remarkable 

 and important deposit, the " Boulder Bed," is always found to exist. 

 This " Boulder Bed " has been identified all over Donegal, Mayo, and 

 Galway in varying thickness, and from its general appearance and 

 characteristics it is probably an older Palaeozoic Glacial Boulder Clay 

 Deposit which marks a possible break between the Ordovician and 

 Silurian series. The boulders in it are almost entirely of an 

 unf oliated granite, unlike any granitic rock at present seen at the sur- 

 face in Ireland. They are angular and sub-angular, and occasionally 

 rounded in form, and but thinly distributed in a fine-grained matrix ; 

 occasionally blocks measuring 3|- feet across can be seen, as in the 

 Fanad area, Donegal. 



The limestone, where seen, always underlies the "Boulder Bed," 

 and is occasionally quite pebbly, as at Carndonagh and other places in 

 Donegal, as well as in Counties Galway and Mayo. The known 

 fossiKferous Bala Limestone rocks in the west of Ireland, at Bossroe 

 and Tourmakeady, at Caherconree, in Kerry, and at Portrane, county 

 Dublin, and elsewhere in Ireland, are occasionally found to be pebbly. 

 It appears to me, therefore, to be a point in favour of the contempo- 

 raneity of those metamorphosed limestones of the west and north-west, 

 and the Bala Limestone of the west, south, and east, and one well 

 ■worthy of further consideration. 



