64 
JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
Above this “ Yellow Sandstone,” which, perhaps, will be best 
called Upper Devonian, comes the Carboniferous Slate, a series of dark- 
bluish gray, sometimes black, slate, frequently in ter stratified with 
hard gray grits. This group is very thin towards the east, but 
thickens out westwards to very large dimensions, being not less than 
5000 feet on the shores of Ban try Bay. The lower part of this mass 
forms a sub-group of hard thick gray grits, in ter stratified with black 
slates, which have been called “ Coomhola grits,” from a valley near 
Glengariff, where they are well seen. The thickness of this subor¬ 
dinate group, at Coomhola and Glengariff, is about 3300 feet. The 
Coomhola grits differ but very little from those of the Upper Devo¬ 
nian. The colour of the Coomhola grits, however, is generally a 
purer gray, while those of the Devonian have a slight greenish tinge. 
The only physical characters by which it is possible in all cases to 
separate the two groups are the occurrence of black slate partings 
in the Coomhola, or Carboniferous grits, and their absence from those 
of the Old Bed Sandstone, whether upper or lower, in which the slates 
between the gritstones are green, yellow, pale gray, and almost all 
colours except black. 
The fossils in the upper portion of the Carboniferous slate do 
not differ, except in the absence of certain forms, from those of the 
Carboniferous limestone. The most usual forms are Fenestella, pro¬ 
bably the F. plebeia , and Encrinites, species of the genera Actinocri- 
nus, Platycrinus, and Poteriocrinus, and even Bhodocrinus, identical 
with those of the Hook limestone and the Carboniferous shales of 
Pembrokeshire. With these, Spirifer disjunctus (Sowerby), and 
Spirifer cuspidatus , occur in great numbers, so that they may be consi¬ 
dered the characteristic shells of the formation, and they are very 
often accompanied by Orthis fdiaria , Strophomena crenistria, Athyris 
squamosa, a species of Productus, and everywhere by the Rhynconella 
pleurodon. A smooth species of Orthoceras, a Nucula, and the Mo- 
diola M‘Adami , occur. In certain localities, especially near Cork, 
the latter shell is very abundant. 
The grit beds in the Carboniferous Slate, and especially in the 
lower part of it, are usually covered with annelid tracks, and many 
of them are permeated throughout by small branched fucoids. The 
nature of these is doubtful, and they may be merely worm tracks, 
but they are well worthy of notice from their great abundance, and 
from their being equally characteristic of the Lower Limestone shales 
in Pembrokeshire. 
