On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain 535 
3. Description oF LOocALiITIEs. 
Before giving a detailed description of the several localities in the British 
Islands in which the Carboniferous Limestone has been proved to contain remains 
of fossil fishes, it may be worth while to briefly summarize what is known of the 
general character and constitution of the formation as a whole. In Derbyshire 
the limestone is a pure, thick-bedded and massive rock, probably two or three 
thousands of feet in thickness with occasional but very thin beds of shale. Similar 
characters prevail in the neighbourhood of Clitheroe, in Yorkshire, and the lime- 
stone has been estimated to attain even a greater thickness than in Derbyshire. 
northwards and southwards of these localities the limestone becomes much thinner 
and gradually assumes a different character. The massive limestone of Derbyshire 
is diminished southwards in Leicestershire to little more than two hundred feet 
in thickness and is intercalated with thick beds of shale; still further southwards 
the coal measures of South Staffordshire rest immediately on the silurian rocks, 
and the Carboniferous Limestone is entirely absent. From Clitheroe northwards 
the limestone diminishes in thickness to 600 feet beneath Ingleborough and a few 
miles further, in Wensleydale, has lost its thick-bedded character and is divided 
into a number of beds of thin limestone with numerous intervening strata of shale 
and sandstone, whilst in Northumberland, still further northwards on the southern 
flank of the Cheviot Hills, the shales and sandstones have increased to an enormous 
thickness and the limestone has almost entirely disappeared, represented only by 
a few thin bands. In Cumberland a similar decadence may be traced, throughout 
the whole of this district, where the base of the thick limestone has been exposed, 
it is found to rest unconformably on the upturned or contorted beds of Lower 
silurian rocks. The junction of the two may be seen to advantage in the 
neighbourhood of the Great Craven faults in Yorkshire; as for example, at 
Monghton Fell in Ribblesdale, at Norber or at Thornton Force beneath Ingle- 
borough. The silurian rocks are in all instances bent and folded at a high inclination, 
the whole denuded down to an even surface on which the limestone is deposited. 
In Ireland the Carboniferous Limestone is very largely developed, and consists 
for the most part of three divisions; there is a thick, pure limestone at the base | 
and the top, and between the two a middle division which is more or less mixed 
with shales or sandstones, the limestone is also impure and earthy. In the 
Kilkenny district the limestone is pure and massive, reaching to two or three 
thousands of feet in thickness. To the southwards and south-westwards it 
thins out and is gradually replaced by shales in counties Waterford and Cork, 
and still further to the south entirely disappears, and its place is taken by 
thick masses of coarse gritstone. Northwards, at Armagh, the limestones are thin 
and divided by beds of shale and sandstone, and towards the highlands of Donegal 
TRANS ROY. DUB. SOC., N.S., VOL. I. 4+ M 
