GEOLOGICAL SOCIETY OF DUBLIN. 
3 
Island, and in a northern and southern direction from the neighbour¬ 
hood of Castlebar on the south, by the Croaghmoyle Mountains, to the 
base of the quartzose mountain of Hephin on the north. 
These three districts comprehend the localities in which this doubt¬ 
ful class of rocks occurs in the north and north-west of Ireland (and I 
may here mention another district containing them, situate to the west 
of Lough Mask, in the counties of Galway and Mayo, which extends 
to the mouth of Killary Harbour); but iu the south they occupy a 
very extensive district, comprehending the south-western portion of 
the counties of Cork and Kerry, and particularly the peninsula of 
Dingle. This latter district has been examined within the last three 
years with great care by the gentlemen employed on the Geological 
Survey of Ireland, under the direction of my friend Mr. Jukes, and it 
is chiefly on the result of my own previous examination of this district, 
combined with the general information obtained from him, that I am 
induced to introduce this matter for discussion in the Geological Society, 
in the expectation that such discussion may eventually lead to a final 
decision in regard to the difficulty of the question at issue, and thereby 
enable me, if necessary, to correct the colouring and the lettering 
which indicate particular classes of rock on my Geological Map of Ire¬ 
land. 
At the Meeting of the British Association of this year, held in Dub¬ 
lin, I brought this subject, in conjunction with Mr. Jukes, before the 
Geological Section, and in a paper which I communicated at the Meet¬ 
ing of 1843, held in Cork, I entered at some length on the discussion of 
the class of rocks to which the reddish-brown sandstone district, situate to 
the north-east of Lough Erne, should belong; and I then generally de¬ 
scribed their unconformity with the red and gray sandstones which form 
the base of the Carboniferous series, and also their apparent conformity 
with the strata of the two small Silurian districts in the neighbourhood 
of Pomeroy and Lisbellaw. I also stated the probability of these 
brownish-red rocks being Silurian, from the analogy subsisting between 
them in the three districts I have mentioned, in two of which we find 
fossils of Silurian age. At the same Meeting, in a communication on the 
lower Carboniferous rocks, I pointed out that at Lisnarrick the Calp 
rests unconformably on the brownish-red conglomerates, while on the 
east and south the latter appeared to conform to the Silurian strata; and 
I observed that the red colour can no longer be considered a test of age, 
as it had been shown that red beds rested on undoubted Carboniferous 
rocks. 
Erom the foregoing it would appear that from an early period I was 
inclined to connect these conformable brownish-red sandstones and 
conglomerates with the Silurian system, rather than to allot them a 
separate place; but, owing to the deficiency of our knowledge as to the 
real relations of the rocks termed Devonian, and the possibility, from 
the fact of their overlying the Silurian, that these rocks might be of that 
age, I was induced to place them provisionally in the Devonian system, 
at the same time distinguishing them from the Bed Sandstones and 
