the Counties of Mayo and Sligo in Ireland. 155 



silver. About eighty years since, another lead mine was wrought at Lug- 

 gawarry, on the north face of the Ox Mountains, near the pass of Carrick 

 na Shouock. The level and some shafts are still open, and the ore was found 

 near the junction of the limestone with the subjacent rocks. Organic re- 

 mains abound in the formation, some occurring in it exclusively, as far as 

 I have examined the midland parts of Ireland. Among these, polyparia are 

 prominent, especially a gigantic species of Cyathophyllum ; and among the 

 shells I have seen two specimens of a very large Euomphalus, armed with 

 formidable spines*, also many species of Productus, Spirifer, and Tere- 

 bratula. In the Hill of Skreen, among the lower beds of this rock, near the 

 junction with the subjacent conglomerates, are some thin strata containing 

 numerous quartz pebbles cemented by limestone; and beneath these are 

 layers containing shells, but no quartz pebbles. In the neighbourhood of 

 Killalla is the following peculiar formation, which I have not observed else- 

 where. It is interposed between the limestone and the older sandstones. 



B. Oolite of the Carboniferous Limestone. 



This deposit, which lies below the limestone from Moyne to Rathrea, 

 varies in colour from iron grey to dark smoke grey ; and is composed of gra- 

 nular concretions not larger than mustard-seeds, but, under the microscope, 

 appear to consist of concentric laminae. Its durability as a building material, is 

 proved by the ruined abbey at Moyne, the arches, pillars, and smallest 

 mouldings of which, retain the most delicate touches of the chisel. Marine 

 exuviae occur in this rock, but so comminuted that the genera are scarcely 

 determinable. It contains also, though rarely, carbonized and pyritous, 

 vegetable remains, resembling reeds and the leaves of the Iris ; also nodules 

 of black shale containing particles of pitch coal. Sometimes cavities occur, 

 lined with arragonite, in fibrous radiated concretions. The beds are fre- 

 quently separated by layers of brownish slate clay, varying in thickness, 

 and interspersed with fragments of black slate clay, not at all water-worn. 

 This oolite, as already stated, is very limited in extent, being found only from 

 Moyne by Killalla to Rathrea. In some parts of the county of Sligo, the 

 lower beds of the carboniferous limestone are highly crystalline, and much 

 resemble this rock ; but a magnifier immediately detects the absence of the 

 spherical concretions. 



At the outcrop of this deposit along the shore, between Killalla and the 

 Abbey of Moyne, is a breccia composed of angular fragments of oolite, im- 



* A species somewhat analogous is figured in the 2nd part of Prof. Phillips's Geology of York- 

 shire, PI. XIII. fig. 5. 



X 2 



