TRANSACTIONS OP THE SECTIONS. 47 



The mica-slate district extends northward for a distance of eight miles to Black- 

 water bridge, where it terminates, and is succeeded, in an unconformable position, by a 

 remarkable suite of Silurian rocks. 



The first member of this series consists of a breccia composed of angular fragments 

 of reddish-brown mica-slate, enveloped in a paste consisting of very small fragments 

 of mica-slate. This breccia is stratified, and its thickness is unequal, varying from 50 

 to 150 feet. It is usually succeeded by brownish-red compact quartzose sandstone, 

 which is stratified conformably with the micaceous breccia; its average thickness may 

 be about 250 feet; this sandstone is followed by sti-ata composed of gray compact 

 quartzite about 300 feet in thickness, which, when slightly disintegrated, presents the 

 character of quartzose sandstone. These strata are arranged in rather thick beds, some 

 of which are very fossiliferous. In the line of section the characteristic fossils con- 

 sist of — 



Amphion brongniarti, n. s. Atrypa lacunosa. 



Asaphus latifrons. „ hemisphserica. 



Bellerophon trilobatus? (cast Orthis canalis. 



Orthoceras gregarium. ,, orbicularis. 



,, tenuicinctum. Modiola semisulcata. 



,, virgatum. Favosites polymorpha. 



Turritella gregaria.? Turbinolopsis bina. 



,, obsoleta. ? Tentaculites ornatus. 



But in other localities near the eastern boundary of the Silurian district at Thon- 

 legee, on the northern declivity of Benleva mountain, and at Bohaun, south of Cor- 

 reen mountain, the characteristic fossils are, — 



Amphion brongniarti, n. s. Orthis orbicularis. 



Agnostus tuberculatus. Turritella gregaria. 



Bellerophon trilobatus. Trochus lenticularis. 



Orthoceras gregarium. Atrypa affinis. 



Atrypa hemispheerica. Leptcena depressa. 



,, lacunosa, var. ? Modiola semisulcata. 



,, pulchra. Tentaculites ornatus. 



and several others, with many new species. 



In the line of section the fossiliferous quartzite is succeeded by thick beds of coarse 

 conglomerate, having a base of gray compact quartz, with pebbles varying in size from 

 one inch to one foot or more in diameter, the pebbles being composed of compact 

 quartz, varying in colour from white to dark reddish gray. This conglomerate, which 

 is not fossiliferous, alternates with a compact quartzose slate ; the whole may be about 

 150 feet thickness near Blackwater bridge ; but in other localities it is very thin, and 

 towards the eastern extremity of the district it is altogether wanting. The conglome- 

 rate beds are succeeded by a series of strata of about 2000 feet in thickness, consisting 

 of greenish-gray compact quartzite, and greenish-gray flaggy slate. At Tullyconnor 

 bridge they are followed by a series of beds composed of dark gray clay-slate, alter- 

 nating with gray quartzite, the slate predominating. This series may be about 700 

 feet thick ; it contains numerous fossils, the most important of which are — 



Calymene pulchella. Orthis lunata. ? 



Amphion brongniarti, n. s. ,, orbicularis, 



Orthoceras filosum. ,, plicata. ? 



,, tenuicinctum. ,, sericea. 



„ virgatum. Leptiaena depressa. 



Euomphalus lloydi, n. s. „ euglypha. 



„ perturbatus. Psammobia rigida. 



,, sculptus. Favosites fibrosa. 



Atrypa navicula. ? Tentaculites scalaris. 



Orthis canalis. 

 In the eastern part of the district at Benleva mountain already mentioned, at Kil- 

 bride on Lough Mask, and at Ardaun, north of Lough Corrib, numerous fossils have 

 been discovered in the schistose rock, and nearly in the same position as those which 

 occur in the dark gray slate near Tullyconnor bridge, the most characteristic of which 

 are — 



