58 
PEOCEEDINGS OF SOCIETIES. 
recent shells, to be of very modern origin. The Norfolk drift with Scan¬ 
dinavian pebbles, according to Lyell, also rests, at some points, on a 
fresh-water bed, with shells of existing species; and in the west of 
England boulder formation, as well as the drift of Wales and Scotland, 
are found shells of mollusca that now inhabit our seas. But the Irish 
escars, so far as hitherto known, neither contain fossils of their own, nor 
overlie any beds that discover their age. To account for the former 
circumstances, it would he only necessary to consider the character of 
their materials, when it would he plain that no shell could have resisted 
the grinding action of the moving gravel; hut this would not so well 
explain why traces of the lithodomi, which I have always searched for 
in vain, should he wanting ; and we must, therefore, seek a different 
cause for the absence of shells. I think this may he found in the pro¬ 
bable fact that little, if any, of the drift that has been left behind by 
the waters, ever lay at the surface of the former sea bottom, the upper 
parts of which have been swept away beyond our ken; and the drift 
that we now see was derived from rocks that were situated at a depth 
to which no mollusca ever reached. 
The escar drift is well developed in the west of Ireland ; and in an 
extensive district which I have closely examined, in the west of Gal¬ 
way, and the eastern parts of Mayo, I think I have succeeded in disco¬ 
vering evidences of two other drifts. I will now venture to describe 
all three, giving them distinctive names for clearness sake, and classi¬ 
fying them in the order of succession upwards, as follows :— 
1. The clay drift. 
2. The great boulder drift. 
3. The escar drift. 
The movement of the first I believe to have been from a point be¬ 
tween the south-east and the west; of the second, from a point between 
the north and the west; and of the third, from the south-west. 
The “clay drift” forms prominent cliffs on the coast near Barna, about 
two and a half miles S. W. from Galway (Ordnance sheet 93); and 
similar ones occur at intervals round the eastern and southern shores of 
the bay to Ballyvaughan, in the county of Clare (0. S. 2). At Barna 
its great mass consists of limestone boulders and clay; but it is sparingly 
intermixed with granite, by which general name I will call the various 
syenitic rocks of Galway; and, at first view, one would see nothing 
remarkable in the mixture, as the cliffs are situated in a granite country. 
However, on a closer inspection it is easily perceived that the peculiar 
species of granites which are found in those cliffs are not the native 
rocks of the neighbourhood ; nor have I found them in situ in any part 
of the igneous district of West Galway. The inference is, that they 
came from rocks that are still hidden beneath the waters of the bay; 
whence alone the drift could arrive without containing some of the 
granites that now form our dry land. But that it did not come from 
those parts of the bay which lie to the east or south-east, is shown by 
the drift of the Aughinish cliff (Clare 0. S. 3), which is composed of 
limestone boulders imbedded in a tenacious clay, without a trace of the 
