178 JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
tation has run down over the face of the cliff; it has evidently drained 
from the guano above, and has also infiltrated the whole of the up¬ 
per portion of the rocks, rendering the identification of them very 
puzzling. Through the kindness of Professor Haughton, I am enabled * 
to lay before you an analysis of the white veins which penetrate 
the sandstone:— 
Per Cent. 
Water,. 4*80 
Silica,.1*74 
Alumina,.1*80 
Sulphate of Lime, ........ 90*74 
99*08 
Though scarcely within the scope of such a paper as this, as 
being of much more recent origin, it will be hardly proper to pass 
over the guano beds unnoticed. Their structure is easily seen here, 
and is as follows:—Conical ridges, in one case attaining the height of 
200 feet, regularly stratified; the strata of various thicknesses, not 
following the lie of the subjacent rock; the strata of one hill crop¬ 
ping out at the sides, originally, apparently, continuous with those 
of another, and running horizontally; but I have entered so fully 
into this subject elsewhere (Journal of the Royal Dublin Society, 
vol. i. p. 89), that further structural description were superfluous. 
These beds rest either on the porphyritic granite, the sandstone grit, 
green sandstone, or coarse conglomerate; when the latter, the lower 
beds of the guano is filled with boulders, which, though quite hard and 
rounded when exposed, soon crumble aw r ay, and become filled with 
cracks containing crystals of carbonate of ammonia. Lumps of car¬ 
bonate of ammonia and of a mixed carbonate and phosphate of am¬ 
monia occur, the former as angular broken pieces, the latter as botry- 
oidal rounded nodules in regular pockets in the guano. 
The Middle Island does not call for particular description; the 
masses of trap, as already stated, are much larger here, composing 
the entire cliffs on the eastern side of the island. The island runs 
about N. E. and S. W. On the South Island the cliffs around are 
more continuous than in either of the other islands, and there is but 
one sandy bay, si tuated on the east: this, a great number of rocks ren ders 
absolutely inaccessible. The channel which separates it and the Middle 
Island is, as already stated, sheltered; the coast of the South Island 
here is precipitous, with a broad shingle beach at its base. Access 
