RESEARCHES AMONG THE PALAEOZOIC ROCKS OF IRELAND. 133 
ing in Silurian fossils; but the relation of these with the brown- 
stone strata cannot be determined, as there are numerous protru¬ 
sions of porphyritic rocks, which interrupt the succession. Simi¬ 
larly with the Tyrone district, the Old Red Sandstone and limestone 
at Boyle, and at Ballaghaderreen, lie unconformably on the brown- 
stone, along its southern border. 
3. About Castlebar, ordinary Old Red Sandstone is abundant. 
So far as physical aspect goes—that is, brown colour and excessive 
hardness—there is a district north-west of this town, lying between 
Lough Conn and Newport, which I would put in the brownstone 
division. I have not had opportunity, however, to work up this 
district, either for succession or fossils, by any more than a slight 
examination. A small district of similar character occurs on the 
south side of Clew Bay, and west of Louisburg. 
4. The Killery Harbour district comes next. It is situated in 
the county of Galway. On the road from Clifden to Westport, at 
Blackwater Bridge, three miles south of Killery Harbour, a succes¬ 
sion of strong conglomerates, gray grits, and gray slates, containing 
an abundance of Silurian fossils, lie unconformably upon strata 
composed of mica slate, with alternating groups of gray crystalline 
limestone and quartz rock, all without fossils; and, what is remark¬ 
able here is, that, in general, a band of brownstone forms the base 
of the Silurian district. This band varies from 200 to 300 feet in 
thickness and is surmounted by gray and green grits, and slates, 
which abound in Silurian fossils, with accompanying bands of 
coarse conglomerates. The district extends, on the south side of 
Killery Harbour from the ocean eastwards, in irregular form, to 
Lough Mask and Lough Corrib, and in all the middle and eastern 
parts the brownstone band forms a conspicuous base, and gene¬ 
rally an index to any locality where fossils may be expected, as 
the fossiliferous beds overlie it immediately. I may add that, in this 
district, as well as at Dingle, there is an enormous thickness of green 
and gray grits and slates, amounting to many thousand feet, over 
the principal fossiliferous band near Blackwater Bridge just alluded 
to. The beds of rock in general dip and accumulate from this loca¬ 
lity to the north-east towards Toormakeady, on the west side of Lough 
Mask; and then, as if to tie all this mass of strata into one great 
parcel, a thin band of limestone occurs, near the top at Glensaul, in 
which Silurian fossils have been found,—this being a parallel case 
with the Brandon Head section, already described. 
