172 
THE GEOLOGIST. 
Our present genial temperature, as correctly remarked by Lyell, is ex- 
ceptional, and it appears to be in some measure due to the Gulf 
Stream ; but, as maintained by Eamsay, some general cause must have 
operated in producing the extreme frigid climate of the Glacial period, 
considering that it prevailed over an immensely wide geographical 
area, irrespective of the area being successively under continental and 
oceanic conditions, as it was during the first and second epochs. 
Apparently, the climate was somewhat less rigorous towards the close 
of the second epoch, and during the one to which I shall next advert. 
Second (subaqueous) epoch. — I have considerable doubt that ter- 
restrial, lluviatiie, or littoral animal life existed, except very partially, 
in the British area under the severe conditions of temperature of the 
first (subaerial) epoch ; and I am disposed to apply a similar doubt to 
the early division of the one under consideration. This is the reason 
why I have excluded fossiliferous deposits from the two stages re- 
spectively forming the dose of the subaerial, and the beginning of 
the subaqueous epoch. 
The shells found by Trimmer on Moel Tryfaen (1400 feet in height), 
and named by Forbes, do not positively indicate an Arctic climate; 
but this may be accounted for on the supposition that the deposit 
containing them is of littoral origin. Deposits formed, contem- 
porary with the " Moel Tryfaen Shell Drift," at the bottom of a deep 
sea, would contain shells of a decidedly Arctic character. At the 
present time, the littoral zone of the west coast of Ireland is te- 
nanted by southern species {Diodonta fragiJis, Avicula Tarentina, 
Circe minima, etc.) ; while in the comparatively deep water (100 
fathoms) of the plateau, already noticed, there occur the following 
subarctic species, Leda pygmcea, Linwpsis aiirita, Macandrevia cra- 
nium, etc. The " Airdrie (Lanarkshire) Tellina caJcarea clay " may be 
regarded as the equivalent in geological time of the " Moel Tryfaen 
Shell Drift ;" but formed in deep water. 
The removal of blocks from low to high levels, in some cases 
several hundred feet, by the action of shore ice on a gradually sub- 
siding coast may be referred to the first halt' of the epoch, though I 
am disposed to think that the same phenomenon, but on a smaller 
scale, was also produced by land ice during the preceding epoch. 
The remarkable broad terraces, deeply cut out of limestone beds 
(Carboniferous), characterizing the waving slopes of the Clare Hills 
(1000 feet in height) on the south side of Galway Bay, have evidently 
been formed, as the land rose out of the sea from a depth of not 
less than 1000 feet : every terrace indicates a stoppage in the up- 
rising.* It is impossible to conceive that these terraces were formed 
in the subsiding stage of this epoch, or during any portion of the 
preceding one : there is also considerable difiiculty in the way of sup- 
* I noticed tliese terraces at tlie Dublin meeting of the British Association, in 1857, • 
in connection with the remarkable jointing associated withthein. An abstract of a paper, 
which contained a further notice of this jointing, is given in the British Associatiott 
Report of 1857. Professor Jukes has also noticed the terraces and jointing of the Clare 
Hills in his 'Manual of Geology,' .2nd edit., 18G3. 
