66 
JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
sandstones, more or less interstratified with black or dark gray slate, 
intervenes between these two series, physically more connected with 
the base of the Carboniferous system, but palseontologically distinct. 
This group contains the characteristic plants of the Upper Devonian, 
and some at least of the shells of the Carboniferous limestone, toge¬ 
ther with numerous species, especially of the Avicula and Cucullasa, 
peculiar to itself. Some facts, not yet fully worked out, would in¬ 
dicate a still closer connexion with the Carboniferous Fauna. 
These beds, whether they be eventually identified with the 
typical Yellow Sandstone of Dr. Griffith, as developed in the north 
of Ireland, or whether that may be more truly represented by the 
Carboniferous slate above them, may still remain as a separate group, 
either as lowest Carboniferous, or uppermost Devonian. In the mean¬ 
time the authors prefer to leave them under the designation, in the 
south of Ireland, of the Coomhola grit series. They are clearly the 
equivalents of the Marwood sandstone of Sedgwick and Murchison, 
a group which has been recently shown by one of the authors to 
underlie the Carboniferous slate of North Devon.* 
As an instance of the partial and local development of these 
rocks, the authors describe the great change to be found in them 
in the Kenmare Valley, only ten miles north of Glengariff, in a 
straight line. At Roughty Bridge there is not a greater thickness 
than 50 or 60 feet between the red slates and sandstones of the upper 
Old Red, and the solid crinoidal limestones of the Carboniferous lime¬ 
stone. These 50 or 60 feet consist of dark gray slates above, and 
thick gray and greenish grits below, the very uppermost beds of slate 
having calcareous courses and fossiliferous bands, the organic remains 
in which are true Carboniferous fossils. This diminution in thickness 
in the Carboniferous slate group, from 5000 to 50 or 60 feet in the 
course of ten miles, is not an apparent diminution, the result of faults 
and dislocations, but a real one. The beds are all excellently shown 
in several convolutions round a small separate trough of limestone, 
distinct from the main mass of limestone of the Kenmare Valley, 
which little trough runs for about half a mile east of Roughty 
Bridge, as shown by Mr. W. S. Willson in his recent survey of the 
ground. 
P. S. March, 1856.—Since the above was written, the authors 
are more decidedly inclined to look on the locally developed group, 
* Journal, Geol Soc. London: Anniversary Address, 1855. 
