ON THE GEOLOGY OF THE LAKE DISTRICT OF KILLARNEY. 99 
bedded, dark gray, finely crystalline, and occasionally compact with 
crinoid fragments and other fossils; and these beds rapidly graduate 
down into the Carboniferous Slate, as we proceed still further to the 
west. 
If therefore we take the thickness of the limestone, from the top 
of the first siliceous beds observed at Dundag Bay to the top of the 
Carboniferous Slates, we have a total amount of 800 feet; this does 
not include the upper beds to the east in Muckross Demesne, the 
thickness of which is nowhere ascertainable. At the entrance to 
Coolough Bay, west of the copper mine, the Carboniferous Slates are 
well seen. They average about 250 feet in thickness, and dip south¬ 
wards at 40°. In general character they consist of dark gray slate 
beds, with a few thin crystalline limestones, thin gray grits, and gritty 
slate layers, all more or less fossiliferous. The most common fossils 
are:— Ortliisfiliaria , Strophomena crenistria , Spirifer disjunctus, Athy- 
ris planosulcata , Fenestella plebeia, and stems of Actinocrinus. At 
the base of the section, and resting on the upper Old Red, there is a 
set of thin gray grit layers and gritty slates, almost devoid of fossils, 
and probably occupying the position of certain well-marked beds in 
the Bantry Bay section, termed by Mr. Jukes, Comhola grits. 
From Coolough Bay the Carboniferous Slates strike westerly, with 
the same dip as last observed, till they cross over from Muckross 
Peninsula (south of Brickeen Bridge), on to Brickeen Island, where 
they, as well as the upper Old Red beds, are cut off abruptly by a 
N. and S. fault, which he named the Brickeen Island fault; and here 
the Carboniferous Slates and Limestones of Muckross terminate to 
the west. 
Returning now to the marble quarries, and taking those peculiar 
beds as a well-marked geological horizon, they can be traced east¬ 
wards for the distance of 1200 feet, when they abut against the 
Doo Lough fault, and are shifted northwards about 250 feet by the 
fault which is a downcast to the N. E.; where the line of this fault 
crosses the gray compact limestone, underlying the marble layers, 
the former is changed to a light brown dolomite. He remarked that 
the Doo Lough fault had a probable strike of N. 55° W., traversing 
obliquely across Muckross Peninsula from the small promontory on 
the south close to the Devil’s Island, right through the centre of 
Doo Lough, and from thence into the small rocky inlet west of 
Ardnagluggen Point, on the north shore of Muckross. 
