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 G-ulf 

 Stream ; but, as maintained by Kamsay, 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, fluviatile, 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 close 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 fragilis, 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 ])ygmcea, Limopsis aurita, Macandrevia cra- 

 nium, etc. The " Airdrie (Lanarkshire) Tellina calcarea tclay " may be 

 regarded as the equivalent in geological time of the " Alo el 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 half 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 difficulty in the way of sup- 



* I noticed these terraces at tlie Dublin meeting of the British Association, in 1857, 

 in connection with the remarkable jointing associated with them. An abstract of a paper, 

 which contained a further notice of this jointing, is given in the British Association 

 Report of 1857. Professor Jukes has aJso noticed the terraces and jointing of the Clare 

 Hills in his ' Manual of Geology,' 2nd edit., 1862. 



