GEOLOGICAL SOCIETY OE LUBLIN. 
18 
our path will remain rugged and thorny, notwithstanding every attempt 
at solution. 
In the commencement of my communication I referred to a certain 
analogy which might exist between the reddish-brown rocks, which 
conform to the Silurian of the north of Ireland, and certain rocks of the 
south, which it will now be seen are the Glengarriff grits; both occupy 
a p^ition unconformable to the overlying rocks, and conformable to the 
Silurian beneath (at least as far as Dingle is concerned); and I may re¬ 
mark that this is the case, whether the Silurian rocks are upper or 
lower. Then again, without attaching undue importance to it, a consi¬ 
deration never to be overlooked is, that their lithological composition is 
not dissimilar, consisting, as both do, of reddish-brown sandstone, firec- 
ciated conglomerates, reddish and occasionally green shales with cal¬ 
careous beds; though in the northern rocks the brownish-red colour 
prevails, the greenish strata being less frequent. We have also inter- 
stratilications in both of beds having an igneous origin, the volcanic 
ash of Sir H. De la Beche; and though the analogy fails in regard to the 
typical Glengarriff grits, inasmuch as the northern rocks cannot be com¬ 
pared with them, in respect to the conformity of the latter with the 
true Old Bed Sandstone (as probably no equivalents of this formation 
occur in any part of the north of Ireland ); yet, notwithstanding this, I 
should say we have a double case in favour of the probability that the 
Glengarriff rocks will rather be of Silurian than of Devonian age, and I 
think that it will at all events be admitted, that however the case may 
ultimately be decided, yet that I was sufficiently justified in the classi¬ 
fication, which I have made on my Map, of the Glengarriff grits of the 
two more southern promontories, as well as those of the peninsula of 
Dingle, especially in the absence of fossiliferous evidence, and in the pre¬ 
sence of the formidable inconsistency in position which I have endea¬ 
voured to explain. Indeed, as I before observed, whatever they may 
be, it will be impossible to class them with the Devonian series, at least so 
long as that term remains as a synonym of Old Bed Sandstone. I may 
further be allowed to say, that in the analogy which I have endeavoured 
to establish between the rocks of the north and those of the south of 
Ireland, I am not to be understood as punctiliously asserting exact iden¬ 
tity in their position, the brownish-red rocks of the south being possibly 
higher in the series than those of the north, my argument being, that 
both are of Silurian age (at least, as that term has been hitherto under¬ 
stood), whether to be classed, the one with the upper, and the other with 
the Lower or Cambro-Silurian. 
As a short and striking exemplification of the difficulty presented 
by these rocks, I might suppose the case of two observers acting inde¬ 
pendently, who subsequently enter into conference relative to the investi¬ 
gations which each had made. One of the parties, who had examined 
the district north of Dingle Bay, would, I should say, think he had an 
irresistible case in favour of the Silurian age of these rocks, while the 
other, whose observations had been limited to the district south of the 
bay, would as strongly maintain their Devonian character. XJpon a 
