518 Scientific Proceedings, Royal Dublin Society. 



between the later less altered rocks and the rocks of the older series — gneiss with their 

 associated schists (Gartan series). This unconformability in connexion with those- 

 previously found by Griffith to the north-east, in the Glen valley, and to the south- 

 east, between the rocks of the Slieve Gallion district and those to the northward, com- 

 bined with M'Henry's discovery of Arenig fossils in the " Gartan series," ought to 

 make the geology of at least Ulster quite plain ; — the gneiss and associated " Gartan 

 series" being the equivalents of the Arenig and Cambrian, while the later metamorphic 

 rocks represent the upper part of the Ordovician and more or less of the Llandovery {May 

 Hill sandstone or Passage beds), the lower portion of the Ordovician (Llandeilo) being 

 absent in this province.] 



The Cambrians or Arenig of Antrim (?), Donegal, Leitrim (?),. 

 Sligo (?), Mayo, and Gal way are all more or less altered into 

 schist, gneiss, or even granite ; and in these, at the present time, 

 no fossils are recorded, except the recent finds in the rocks of the 

 Co. Donegal. In Co. Galway they are found in the Ordovicians, 

 but not in the underlying Arenigs or Cambrians (?). In places, 

 especially in the Co. Donegal, some of the gneiss and quartzyte are 

 very little changed, but in general all the arenaceous rocks are 

 more allied to quartzyte or quartz rock (greisen) than to sandstone 

 or grits. 



In Dublin, Wicklow, and "Wexford, some of the Cambrians are 

 metamorphosed, especially in the latter county, where, to the 

 south-east, they are changed into gneiss and granite ; but in 

 places in them are quartzyte and quartz rock (greisen), and in the 

 unaltered portion grits and sandstones. 



ORDOVICIAN and LLANDOVERY. 



[In the Table of Geological Strata, " Metal Mining " (ante -p. 204), the Passage- 

 beds between the Ordovicians and Silurians are called " May Hill Sandstones," or 

 "Llandovery." In this Paper the latter name will be used. In Clare, Tipperary,. 

 and south-east Galway, the Llandoveries are more nearly allied to the Ordovicians ; 

 but in the Dingle promontory, Co. Kerry, they are joined on below the Silurians.] 



Many of these rocks are metamorphosed, as more fully men- 

 tioned in the descriptions of the counties. Some of the grits and 

 sandstones are capable of dressing well ; but only a few of them 

 are now in request for cut-work purposes, as the younger and 

 softer stones are preferred. They were, however, used in many 

 of the early structures, and proved good and durable stones. They 

 were also used in many of the Pre-historic megalithic structures, as 

 they were capable of being raised in massive slabs. 



