90 SEVENTH REPORT—1837. 
localities in the line of section, the carboniferous limestone series is 
succeeded by the mill-stone grit formation. In Cuilceagh Mountain, 
where the series is best developed, the lowest member consists of three 
great beds, or successions of beds, of yellowish white quartzy sandstone, 
having beds of black shale interposed between each ; these beds amount 
altogether to a thickness of 500 feet: they are succeeded by a series 
of beds composed of black shale, which in the lower region of the 
mountain alternate with dull grey earthy limestone, containing varieties 
of Producte, Spiriferee, Orthoceras, &c. 
As we ascend, the limestone beds gradually disappear, and in lieu of 
them we find the shale to alternate with thick beds of argillaceous iron- 
stone, and occasionally with septaria of ironstone; the shale beds con- 
tain a profusion of fossils, the most abundant of which is a variety of 
Posidonia, but several species of Goniatites, and a remarkably small 
species of Orthoceras also occur. 
Still continuing to ascend, the ironstone beds become thin and at 
length disappear, and the upper portion, amounting to a thickness of 
about 250 feet, consists altogether of fine-grained black shale, contain- 
ing organic remains, but particularly Posidonia, but not so abundantly 
as in the lower beds, which alternate either with the impure limestone 
or the ironstone. 
This great shale, which is altogether 700 feet in thickness, is suc- 
ceeded by an accumulation of beds of yellowish white sandstone, about 
250 feet thick; in the lower portion, next the shale, the sandstone beds 
are thin, and alternate with sandstone, slate, and shale ; the upper con- 
sists of thick beds of yellowish white quartzy sandstone, some of which 
are rather coarse grained, and assume the true character of mill-stone 
rit. 
‘i This rock, which forms the summit of Cuilceagh Mountain, and is 
elevated 2188 feet above the level of the sea*, occasionally contains 
vegetable organic remains, particularly some varieties of Stigmaria. 
In the line of section to the west of the Valley of the Shannon, the 
mill-stone grit beds are succeeded by a series of beds, consisting of 
shale and sandstone, with bituminous coal, amounting altogether to 200 
feet in thickness. 
In shale beds throughout contain casts of Posidoniz, Producte, Or- 
thoceras, and occasionally a very minute variety of Trilobite ; and it is 
remarkable that the whole of the fossil organic remains which occur in 
the upper members of the series above the coal, are unusually minute 
in their dimensions, so much so as to give rise to the idea that they be- 
long to a dwindled species which existed possibly in brackish water, 
which, being uncongenial to their nature, prevented their full develop- 
ment. 
(In illustration of this paper the author exhibited his large geolo- 
gical map of Ireland.) 
* Ordnance Survey. 
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