KiNAHAN AND Baily — Report on Eocks, 8fc. 495 



This tract is bounded on the southward by a fault with a down- 

 throw to the south ; south of which, is a second long narrow tract, 

 extending from Loughs Mask and Corrib to the Atlantic, on the south, 

 of Killary Bay. In this area the rocks are, for the most part, of the 

 "grey and green type"; but in places, as subordinate groups, some- 

 times coming in quite suddenly, and usually below, are rocks of the 

 '■ Lower Old Eed Sandstone" type ; but the most conspicuous are the 

 " Salrock slates," above, and probably at or near the same geological 

 horizon as the " Louisburgh beds." A peculiarity connected with 

 the "Salrock slates" is that, although the latest Silurian group in 

 the county of Galway, the characteristic fossil is pronounced by 

 Davidson to be of an English Upper Llandovery type. To the west 

 of this tract, above the eurites, which are on the same geological 

 horizon as those just mentioned as occurring at the base of the 

 Mweelrea and Toormakeady rocks, there is a zone carrying Caradoc- 

 Bala fossils ; while below this zone the fossils are of species charac- 

 teristic of the Upper Llandovery and Wenlock ; while to the eastward, 

 on this lower horizon, in the neighbourhood of Loughs Mask and 

 Corrib, the fossils have been pronounced by Salter, Harkness, King 

 and Baily, to be of types similar to the English Wenlock and 

 Ludlow. 



As the bedded eurites with their associated tuffs occur both north 

 and south of the great fault that separates this tract from that to the 

 north, it wo aid appear that, although the rocks in the two areas were 

 being accumulated at the same time, yet it was under very different 

 circumstances, as to the depth of the sea and the animal life in the 

 different portions of it. The changes in passing from north to south 

 are very sudden, while those from west to east are more gradual : 

 this is even more striking if we also take in the rocks farther north- 

 ward. If a line be drawn from Croagh Moyle to Lough Corrib, the 

 rocks at the northern end are the Croagh Moyle conglomerates, next 

 are the Toormakeady conglomerates, with the fossiliferous limestones 

 at their base (Caradoc-Bala fossils), and immediately south of them 

 are rocks containing Wenlock and Ludlow fossils. Along a line from 

 Mulrany, on the north side of Clew Bay, to the south side of the 

 mouth of Killary Bay, the rocks exhibit even greater peculiarities, as 

 shown in the following Table : — 



Mulramj. — Arenaceous rocks principally. 



Louuhurgli {north). — Red argillaceous shales. 



Louisburgh {south). — Bed argillaceous and arenaceous 

 rocks interstratified. 



Creggaunbaun. — Green and grey fossiliferous rocks — 

 ("Wenlock type). 



Mweelrea. — Eed arenaceous and green argillaceous — 



the latter fossiliferous (Caradoc- 

 Bala types). 



