TRANSACTIONS OF THE SECTIONS. 89 
wacke slate, and are considered to form the first or lowest member of 
the carboniferous limestone series of Ireland. 
In other localities, particularly in the county of Donegal, north of 
Ballyshannon, the strata belonging to this, the lowest members were 
stated to be of much greater thickness, and to contain with the lime- 
stone beds alternations of coarse-grained conglomerate, having a yel- 
low or brownish-yellow base. 
At Belturbet, in the line of section, the yellow sandstone series is 
succeeded by the lower limestone, which consists of a succession of beds 
of carboniferous limestone, more or less pure, and varying in colour 
from light smoke grey to dark blueish grey; these strata amount to a 
thickness of 350 feet in the line of section. 
In other localities in Ireland the lower limestone contains abundance 
_ of black and occasionally grey and reddish mottled marbles of various 
tints, and the whole series abounds with marine fossils similar to those 
which occur in the mountain limestone of Derbyshire, north of York- 
shire, Northumberland, &c. 
. Above the lower limestone we have a series of beds, consisting of 
alternations of black or dark grey shale, dark blueish grey impure lime- 
stone, and yellowish and occasionally reddish grey sandstone, altogether 
400 feet in thickness. 
These peculiar strata, which occur also in the limestone formation in 
the neighbourhood of Dublin, have received the name of Calp from 
Mr. Kirwan, and Mr. Griffith adopted that name to distinguish this 
particular division of the carboniferous limestone. 
In the line of section, the calp series which succeeds the lower lime- 
stone to the west of Belturbet occupies the country as far as Ballycon- 
nell, situated at the base of Slieve Rushin Mountain, where it is suc- 
' eeeded by the upper or splintery limestone, which in this mountain is 
420 feet in thickness; while in Cuilceagh Mountain, situated to the west 
of Swanlinbar, it is 600 feet in thickness. 
The upper or splintery limestone is distinguished from the lower by 
its numerous crags and mural precipices, which often present the cha- 
racter of rude columnar facades; it is usually cavernous, and the 
streams falling from higher elevations are frequently lost in fissures, 
and flow through subterranean channels, till at length they burst forth 
from the lower strata of the series, and flow down the more gentle de- 
clivities of the calp shale beneath them. 
The Great River Shannon has its source in a cavern of the upper 
limestone, which is situated at the western base of Cuilceagh Mountain, 
at an elevation of 342 feet above the level of the sea. 
_ This limestone is equally abundant in fossils with the lower, and 
nearly the whole of the species and varieties which occur in one have 
equally been discovered in the other. 
The splintery limestone forms the upper member of the carbonife- 
rous limestone series, which, in the line of section exhibited, amounts 
to a total thickness of 1750 feet. 
On the summit of Slieve Rushin, and at the Cave of Pulgulm, situ- 
ated on the eastern declivity of Cuileeagh Mountain, and several other 
