42 REPORT—1843. 
north coast of Mayo derived from the Ox Mountains, also situated to the south,— 
we arrive at the conclusion, that at least in the localities mentioned the current has 
been from the south, and nof from the north-west, as has probably been the case in 
other districts of Ireland. 
On the Lower portion of the Carboniferous Limestone Series of Ireland. 
By Ricuarp Grirritn, £.G.S, 
Referring to his communication at the Manchester Meeting (Report for 1842), the 
author stated the subdivisions of the series to be described in the following descending 
series beneath the millstone grit:—1.The Upper Limestone. 2. The Limestone 
Shale, or Calp. 3. The Great, or Lower Limestone. 4. The Carboniferous Slate. 
5. The yellow or Lower Carboniferous Sandstone. 
1. The Upper Limestone.—Its average thickness may be about 600 feet. It con- 
sists of light gray limestone, alteruating near the top with gray flinty slate and occa- 
sionally dolomite. The lower beds frequently contain disseminated rounded masses 
of gray and black Lydian-stone. It presents numerous mural escarpments, many of 
which are cavernous. It is very fossiliferous, and the fossils correspond nearly with 
those of the carboniferous limestone of England, though many are peculiar to it. 
2. The Calp is distinguished as presenting a succession of beds of dark gray shale, 
alternating with dark gray impure argillo-siliceous limestone. This group, when per- 
fect, is separable into three parts,—the upper and lower shales, and an intervening 
yellowish-gray sandstone. The average thickness of the whole may be about 1000 
feet, though in some localities it amounts to 1800 feet. It contains numerous fossils ; 
those found in the fine shale beds differ from the upper limestone, the most charac- 
teristic being several varieties of Posidonia. 
3. The Great or Lower Limestone occupies a large portion of the surface of Ireland. 
Its colour varies from light to dark gray, and its structure is usually less crystalline 
than the upper. The lower beds are frequently dolomitic, and occasionally oolitic. 
This group is more abundant in fossils than either of the foregoing, and contains 
nearly the whole of those found in the two upper members of the system, with the 
exception of Posidonia; its average thickness may be about 1000 feet. 
4, The foregoing comprehends the whole of what was formerly considered to be- 
long to the carboniferous limestone of Ireland, the strata beneath having been pre- 
viously included in the Old Red Sandstone; but in his paper of the preceding year, 
he was enabled to show, by comparing the fossils in the strata below the limestone 
with those above, that they must be attached to the Carboniferous, and not to the 
Old Red or Devonian system. 
These lower members have been subdivided into two, the carboniferous slate and 
the yellow sandstone. 
The whole list of fossils at present discovered contains 925 species without fishes 
or plants, of which 359 are new and have been figured (these are exclusive of those 
contained in the Ordnance Geological Memoir of a part of the North of Ireland, by 
Capt. Portlock, R.E., published during the present year). 
The lower portion of the Carboniferous system of Ireland, to which he has given 
the name of yellow sandstone, to distinguish it from the old red which lies beneath, 
is much more fully developed in the North of Ireland than in the South; some very 
fine sections may be examined in detail on the north coast of Donegal Bay; also on 
the northern shore of Lower Lough Erne, north-east of Pettigoe; likewise between 
Balderig Bay and Killala in the county of Mayo; in the valley of Ballinascreen near 
Maghera in the county of Derry, and many other localities. 
. 
He first proceeded to examine the section near Ballycastle in Mayo, and said that 
the micaceous quartzite, belonging to the mica-slate of Erris, is succeeded uncon- 
formably by strata of red sandstone, rather fine-grained, alternating with red and 
dark green shale, and occasionally with yellowish-gray sandstone and impure gray 
limestone. These beds are 650 feet thick; the dark gray shales and limestones con- 
tain fossils; the shales, Cythere, Modiolez, Nucula, Cypricardia, &c., many of which 
are peculiar to them ; the limestones contain the usual Brachiopoda and corals which 
are found in the upper members of the series. Ascending in the series, beds of dark 
gray limestone, frequently arenaceous, occur, alternating with dark gray, red and 
bP See FE ae ee 

