ON THE GEOLOGY OF THE LAKE DISTRICT OF KILLARNEY. 101 
the district, he remarked that the Lower Lake of Killarney is formed 
almost entirely in the limestone ; Ash, Island, Cow Island, and 
Yew Island, are portions of it; but on Rough Island appeared the 
marble and schistose layers first observed at the marble quarries of 
Muckross Peninsula,—a fact of much importance as determining 
the probable position of the Carboniferous Slates and other lower 
rocks at the bottom of the Lake. The rocky masses known as 
Elephant Rock, Table Rock, Crow Island, Otter Island, Jackdaw 
Rock, and Swallow Island, are formed out of the light gray lami¬ 
nated limestones, being portions of those beds which overlie the mar¬ 
ble layers. The next place to the east where the marble layers 
occur is in the farm-yard attached to Cahernane House. From 
the peculiar position of these beds, they are probably brought to 
view by a N. and S. fault, occurring somewhere near the mouth of the 
Flesk River. Local protrusions of lower beds are rendered probable 
in this district by facts first observed by Mr. Du Noyer in the early 
part of 1855,—-namely, a protrusion of upper Old Red in the midst of 
the Carboniferous Limestones, a few miles west of Mallow, at Droma- 
neen Castle on the Blackwater; and, later in the same year, similar 
Old Red beds occurring in the limestones at Kilmacclenyn Hill, five 
miles N.N. W. of Mallow,—-where the former rock forms a low and 
gentle sloping hill, having the latter dipping away from it in every 
direction. 
Leaving Cahernane Demesne, the next place where the marble 
layers are observed is at the low point on Ross Island shore, due 
north of the RoughYsland, and eventually they appear, for the last 
time, on the south-west shore of Ross Island. 
It will be recollected, that tracing out the geological horizon 
afforded by these marble layers is of the utmost importance in de¬ 
termining the relative position of the limestones of the Lower Lake. 
The shaly and cherty limestones forming the western extremity 
of Ross Island are so contorted as to become inverted in dip, being 
folded back over to the north, and consequently dipping S. at various 
angles, forming Y and S-shaped curves; and at O’Donoghue’s Li¬ 
brary, black shales, evidently a portion of the Carboniferous Slates, 
occur; the same beds are observed forming Innisfallen Island, and with 
the same mode of occurrence, as can be well observed on the west 
shore of that island, when the lake is at a low level. Brown or 
Rabbit Island presents higher beds than those last described, the 
