142 
JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
the Eifel limestone; and endeavoured to join those distant frag¬ 
ments together, and make out of them a consistent whole. 
At the meeting of the British Association at Glasgow, last Sep¬ 
tember, in one of the geological discussions, Professor Sedgwick 
said that the Devonian has no base. In this assertion, I believe, he 
cannot be contradicted. No estimate has ever been attempted to 
be made of its thickness,—nor ever can be, as it appears to me. 
I would not have thought it necessary to notice the brownstone 
as I have done in this Paper, any more than the green and gray 
rocks with which it is associated, only for the circumstance, that it 
appears to have been mistaken for the Old Red Sandstone of the 
Carboniferous system,-—there having been no distinction drawn 
between them; and that a considerable amount of confusion has 
crept into the classification of rocks, in consequence of this mistake. 
I have taken pains to describe both kinds, and to point out the dif¬ 
ference between them; and I hope my observations may be useful 
to others who may have better opportunities of prosecuting the in¬ 
quiry, with a view to settle this important question. 
OBSERVATION ON SOME OF THE JUNCTIONS ENUMERATED IN THE 
TABLE OF LOCALITIES. 
1. The junction at Conaghra, five miles W. of Ballycastle, in 
Mayo. Though the dip of the stratified quartz rock on the coast 
here, and the dip of the Old Red Sandstone, are both eastward, and 
not far from the same angle; yet, on close inspection, it will be 
observed that the lowest bed of sandstone covers over the ends of 
several beds of the quartz rock; and, as it proceeds south, mounts 
over the mica slate also, which there overlies the quartz rock beds 
conformably. 
2. Near Bangor, on the road side, there is a good section of the 
Old Red Sandstone, showing its whole thickness at that place, and 
the transition into the black slates and thin limestones which lie 
over it here, and which abound in mud fossils, Nuculse, Modiolse, &c. 
6. At Ballaghaderreen, the rock which underlies the sandstone 
is a brown slaty porphyry, which shows traces of a dip to the north. 
This porphyry fills a flat district four or five miles to the N. W., 
where it is succeeded by the Silurian fossiliferous slates of Uggool. 
12. At Drung the Old Red Sandstone runs out at the shore to 
low water. 
