102 
JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
limestones being less shaly, and the black chert arranged in more 
definite layers. B 
Returning to the description of the Old Red Sandstone, he re¬ 
marked that to the west of Brickeen Bridge the middle and lower 
beds were cut off by the Brickeen fault, and on the west of the 
fault, by an upcast, the purple or middle Old Red is brought to 
abut against the upper, and the Carboniferous Slates with the lime¬ 
stones are completely cut off. Mr. Du Noyer observed that Muck- 
ross Peninsula was a locality of peculiar interest to the geologist, 
as it presented what might be termed an epitome of the entire of 
the Carboniferous and Old Red Sandstone rocks of the south of 
Ireland. The Brickeen Island fault is therefore one of the best 
marked and most important of the district. The Upper Old Red 
is now lost, and it is not till we get on Dinish Island that it is 
again observed, when, by repeated inverted rolls of the beds, it is 
made to spread over the northern, western, and southern portions 
of the island. If we now cross from Brickeen Island to the boat¬ 
house on the Glena shore, under the cottage, we get into quite a 
different set of beds from those we have just left, though the distance 
is only 300 feet, the rocks agreeing in their strike. Along the west 
side of the island we had light greenish-gray grits in abundance, 
with but few dull purple slates; while, on the opposite shore of 
Glena, we can find nothing but soft purple slates and purple grit, 
without a single greenish-gray bed. We have therefore evidence of 
another N. and S. fault, which he named the Glena fault, on the 
west side of which, by an upcast, the upper Old Red is again brought 
to view, to the south of Glena Mount. 
Proceeding south from Glena Cottage, we rapidly pass out of 
the purple slates and grits of the middle Old Red, and get on to 
the upper beds. These can be traced up the wooded stream which 
flows from the south flank of Glena Mount for the distance of 2000 
feet westerly from the fault; leaving the stream from the point 
named, the same beds can be traced still farther for the distance of 
1000 feet, where we come on the purple grits and slates of the 
middle Old Red; both groups of rock having a southerly dip at 
angles varying from 30° to 40°. Here the upper Old Red curves 
round to the east, and after repeated flexures of the beds along their 
line of boundary with the subjacent rocks, they eventually strike 
east, and abut against the Glena fault; all the observed dips over 
