GLENGARIFF GRITS AND SLATES. : 719° 
Silurian beds are highly discordant to the Lower; and from the ab- 
sence of these beds in the centre and east of Ireland, where the 
Lower Silurian beds reach the surface, we may conjecture, after 
making allowance for denudation, that these districts were land sur- 
faces through a portion at least of the Upper Silurian period. The 
physical geology of this part of the British Isles is therefore in har- 
mony with that which obtained in the region of Wales, Shropshire, 
and the borders of the Wye; over this region, as Professor Ramsay 
has pointed out, the Lower Silurian and Cambrian rocks formed a 
land surface at the commencement of the Upper Silurian epoch, the 
extent of which gradually diminished by submergence until it was 
converted into several islets towards the close of that period*. Pos- 
sibly this early land surface embraced St. George’s Channel, the 
bordering districts of Waterford, Wexford, and Wicklow, stretching 
into the centre of Ireland, as around the Galtees, the Silver-mine, 
and Commeragh mountains we find the Lower Silurian beds overlain 
directly by the Old Red Sandstone. The Upper Silurian basin must 
have extended far into the Atlantic, and have been of enormous 
depth in the region bordering the coast of Kerry, while towards the 
north it was bounded by the crystalline metamorphosed Lower Silu- 
rian rocks, which appear in West Galway and Mayo, and enclose the 
Upper Silurian trough of the Killaries and Mweelrea. 
It is possible that the upper portion of the Glengariff series is 
newer than the uppermost of the Ludlow beds. The existence of 
the ** Upper Ludlow bone-beds ” shows that the border districts of 
Wales were but slightly submerged at a time when the Upper Glen- 
eariff beds may have been deposited in deeper waters. The Upper 
Glengariff beds may possibly form the connecting links between the 
Upper Silurian and Lower Devonian series. 
VY. Retations or THE Orp Rep SanpsTonE To THE DinGLE Bens, &c. 
Throughout the whole of the south and centre of Ireland the Old 
Red Sandstone is everywhere unconformable to the rocks on which 
it reposes, while it passes up by conformable stratification into the 
Carboniferous series. In the Dingle promontory it rests on various 
representatives of the Upper Silurian series, from the Llandovery beds 
upwards, in that highly discordant manner so well described by 
Griffith and the officers of the Geological Survey, overlapping many 
thousand feet of strata (see fig. 3). Great indeed have been the 
terrestrial disturbances and the extent of denudation in this part 
-of Ireland between the epoch of the deposition of the Dingle beds 
and that of the Old Red Sandstone. At least 12000 feet of strata 
‘have in some places been removed during this period. Again, the 
Old Red Sandstone wraps round the dome-like masses of Lower 
Silurian beds which rise from beneath the central plain, or sometimes 
rises into higher elevations, crowning the heights of Galtymore 
and forming the grand escarpment of the Commeragh mountains. 
Traced towards the north and east through Waterford and Kilkenny, 
* Physical Geology of Great Britain, 5th edit. Eo 
Cc 
