Paleo-Geological and Geographical Maps of the British Islands. 273 
Distribution of Land and Sea.—At the commencement of the Upper Devonian 
stage nearly the whole of the centre and north of Ireland, the north of Scotland, 
the centre and north of England and Wales, were dry land, but in the southern 
portions of the British Isles and adjoining parts of the Continent there was an area 
of depression. Over the south of Ireland there appears to have been formed a 
fresh-water lake, in which the Old Red Sandstone was deposited in the form of 
shingle and finer sediment drained from off the adjoiming lands formed of Silurian 
and Devono-Silurian beds which had been previously elevated into land over the 
region of Kerry, Cork, and Waterford. The waters of this lake were inhabited by 
numerous fishes and the large mussel, Anodonta Jukesii, while the adjoining lands 
were covered by a luxuriant vegetation, the representatives of which are preserved 
to us in “The Kiltorean beds.” This lake may have extended eastwards into the 
south of England, but in France and Belgium it gave place to marine conditions, 
as the representative strata known as the “ Psammite du Coudroz” are of marine 
origin.* In Scotland the yellow sandstone and conglomerate, with Holoptychius 
and Oyclopteris (Paleopteris) Hibernica, was probably deposited within lacustrine 
waters. 
On the commencement of the Lower Carboniferous stage the sea everywhere 
occupied the submerged tracts, bathing the sides of the uplands and mountainous 
parts, and bringing with it multitudes of marine animals, so that the oldest 
Carboniferous strata in Ireland, England and Wales, and Scotland contain numerous 
marine forms.t During the subsequent epoch of the Carboniferous Limestone the 
depression proceeded, and the sea ascended on the flanks of the uplands until only 
the very highest elevations were left uncovered. Deep sea conditions prevailed 
over the north and south of England and the centre of Ireland, and here the calcareous 
beds were formed in greatest thickness and purity through organic agency. A tract 
of country extending across England, from Shropshire through Worcestershire and 
South Staffordshire, into the eastern counties appears to have remained as a ridge or 
land barrier, separating the basin of the north of England from that of the south, 
as the Lower Carboniferous rocks are absent, or only present as thin marginal 
representatives along this line of country.+ 
In Plate XXVIL., figure 2, the relations of sea and land are indicated, as far as 
possible, during the middle of the epoch of the Carboniferous Limestone. 
It is also probable that the old rocksof the north-west of France were unsubmerged, 
as the little detached coalfields of the centre of that countryrest directly on these rocks 
* Here it contains marine fossils, such as Spirifer disjunctus, Rhynchonella pleurodon, with plants 
Lepidodendron notum, Sphenopteris flaccida, and a variety of Paleopteris Hibermea. Mourlon. Loe. 
cit., p. 88. 
+ See preceding Table of Synonyms, page 272. 
; The existence of such a ridge was first indicated by the late Professor J ukes, and subsequently 
described in “The Coal Fields of Great Britain.” The discovery of Carboniferous Limestone at a depth, 
of 890 feet below Northampton shows that the ridge was south of this spot. Etheridge; Quart. Journ. 
Geol. Soc., vol. xxxviL, p. 231. 
TRANS. ROY, DUB. SOC.,N.S. VOL» I. 2Z 
