GEOLOGICAL SOCIETY OF DUBLIN - . 
61 
sea. The whole sandstone country is full of hills of its own detritus, 
generally in confusion, hut sometimes showing a tendency to lines run¬ 
ning east and west, or S. W. and ~N. E., and with forms elongated in 
those directions. At Cahir (Q.S. 81) limestone drift is found below 
sandstone at a depth of 20 feet, and may be an example of the “ clay 
drift’’ underlying the “ boulder drift.” I have not examined the country 
farther north; but Mr. Griffith has proved a drift movement there, from 
south to north, as far as the sea. I may here remark, that eastward from 
Galway Bay, which would appear to have been the focus of a certain 
amount of divergence, the gravel hills seem to run in a more easterly 
direction. 
The greatest apparent difficulty connected with the separation of the 
drifts lies in distinguishing between the “ clay drift” and the escar for¬ 
mations ; for they might be easily considered as identical and overlaid 
by the “ boulder drift.” The following are the reasons that induced me 
to make the division :—In the first place the “ clay drift” of Galway Bay 
bears only on its surface, and never within it, any materials which can 
be referred to the “ boulder drift;” and the escars, on the contrary, con¬ 
tain, mixed with the limestone gravel, that forms their chief bulk, 
many mica slates, greenstones, and other rocks, which must have been 
previously deposited by it, as no formations from which they could be 
derived lay in the course of the escar drift. In the next place, I think 
that the separation is justified by the appearance of the escar hill-chains, 
whose long unbroken lines suggest the idea that the force which shaped 
them was the last that passed over the surface of the present land; and 
as the “ boulder drift” was subsequent to the “ clay drift,” so the escar 
dfift was posterior to the former, which intervened between both the 
others. 
Though I believe that we have thus sufficient data to prove the ex¬ 
istence of three great drift periods in this district, still there are many 
deposits which it would be impossible to refer distinctly to any one of 
them. Beneath the alluvial flats, where our rivers run slowly in a deep 
channel, we often find a stratum of rounded boulder-stones imbedded in 
blue or yellow clay, and differing in that respect from the materials of 
the escars, which never advance beyond the borders of those plains. The 
rounding of the boulders is certainly not to be attributed to the action of 
the river itself at any period; for we have no reason to believe that the 
waters ever moved with greater velocity in those parts than at present, 
but rather less ; for above the boulders there is generally a stratum of 
marl, and on this, the surface layer of alluvial soil, both containing shells 
of the most delicate structure, in so perfect a state of preservation as to 
convince us that they must have been deposited in almost still water. 
These shells are all recent, including the genera Planorbis, Lymnsea, 
Succinea, Paludina, Cyclas, &c., mixed with land shells; and their in¬ 
habitants must have lived at a time when the river was rather a succes¬ 
sion of lakes, joined by narrow straits, before its waters cut a deeper way 
through the barriers that opposed their course, and, with a diminished 
breadth and reduced level, formed a channel through the lowest part of 
VOL. V.-PROC. SOC. K 
