ON THE GEOLOGY OF THE LAKE DISTRICT OF KILLARNEY. 109 
elevation. The level of this Lake above the sea is 1126 feet, and 
the rocks surrounding it are all purple grits and slates,—the middle 
subdivision of the Old Red Sandstone. Here again is obtained a 
natural section of these beds, amounting to 2238 feet, of vertical 
elevation, but if measured at right angles to the beds which dip, it 
would be increased to fully 3500 feet. Now all the rocks in the 
Hag’s Glen to the north are those of the middle Old Red, and, as 
they dip westerly from 10° to 40°, they, of course, are higher beds 
than those last alluded to; and, consequently, the absolute observed 
thickness of the middle Old Red may be estimated here at 4000 
feet. 
From the foregoing observations it is clear, that in this district 
of the county of Kerry w r e have a development of the middle sub¬ 
division of the Old Red Sandstone (taking the Yellow Sandstone 
of Dr. Griffi th as the upper), which, per se , would be quite suffi¬ 
cient to form the mountain ranges of the Knockmilldowns, the 
Galtees, the Mushera, the Cummeragh, or other Old Red mountain 
ranges in the south of Ireland, supposing the beds to be horizontal. 
Hence we have a strong argument in favour of the supposition that, 
wherever in the south of Ireland purple beds alone form the mass 
of the Old Red Sandstone, they should be regarded merely as the 
middle subdivision of that group. Such appears to be really the 
case, for in the districts of Bally vourney, Gougane Barra, and Inchi- 
geelagh, county of Cork, the green and greenish-gray grits and slates, 
with occasional purple slates, similar to those described as the lowest 
beds of the upper Lake and Black Valley sections,—but devoid of the 
fine conglomeritic layers observed so frequently in the latter rocks,— 
are the lowest beds in all the well-developed sections, and pass gra¬ 
dually and conformably into the purple grits and slates. 
From having examined the Old Red Sandstones in the county 
of Waterford and Wexford, as well as in the county of Cork, at 
Mitchelstown, Mr. Du Noyer stated, that wherever he found it rest¬ 
ing on the Silurian rocks, it lay unconformably on them; that its 
lowestbeds were formed of coarse and fine conglomerates derived from 
the Silurian; that these conglomerates contained jasper pebbles; that 
they were often green in colour; and were split up by green and 
purple grits and slates. Therefore he saw, as yet, no reason why the 
green and greenisli-gray conglomeritic grits, with green and purple 
slates, of the Lake district of Killarney, should be regarded as Silurian. 
