KINO — GLACIAL AND POST-GLACIAL DEPOSITS. 



177 



The formation of the gravel terraces of Glen lloy appears to have 

 taken place in the last half of this epoch — when the land was sub- 

 siding. Had they existed previously, they must have been obliterated 

 by glaciation. Nothing affords a better explanation of their origin 

 than the view originally advanced by Agassiz, and lately adopted by 

 Lyell, that they were formed in a valley converted into a lake by the 

 damming up of its mouth with a glacier which descended from Ben 

 Nevis. Admitting that the Glen Koy terraces have been formed in 

 this way, it must be conceded that the land was at the time gradually 

 yet intermittently subsiding. While the subsidence was going on, it 

 may be safely assumed that the glacier-dam became more and more 

 reduced in height, causing at the same time the level of the lake, 

 water to fall lower and lower, until, finally, both glacier and lake 

 disappeared altogether. Possibly the melting of the glacier was 

 facilitated by the gradual setting in of the more genial climatic con- 

 ditions which prevailed in the succeeding epoch. It is unnecessary 

 to suppose that the land, when subsiding, descended beneath its 

 present level in the last stages of the lake and glacier. 



The way in which the glacier-lake of the Marjelen-see is formed 

 and sustained, that is, by the glacier of Aletsch, as described by 

 Ramsay, may be accepted as a good illustration, on a small scale, of: 

 the origin of the old glacier-lake of Glen Hoy. 



Post- Glacial Period. 



First epoch (subaqueous). — There are several mountain bogs in the 

 west of Ireland containing the remains of rooted trees which could not, 

 under present conditions of temperature, grow at their present eleva- 

 tion. I am strongly inclined to believe that they grew at a lower 

 level. The " Belfast Thracia convexa clay " may have been deposited 

 about the same time in deepish water. 



Second epoch (subaerial). — During this epoch, considerable portions 

 of the submarine area between the south of Ireland and the coast 

 of Spain, and averaging about 200 feet in depth, was elevated above 

 the level of the sea, giving rise to a land-surface which botanically 

 connected these two countries. The connection, although now phy- 

 sically severed, is still maintained, as Forbes noticed in 18-16, by the 

 presence of Asturian plants — Dabeocia polifolia, Pinguicula grandi- 

 flora, Arabia oiliata, Tricliomanes radicans, etc. — in Kerry and Con- 

 □emara. Forbes conceived that the "destruction of the intermediate 

 land took place before the Glacial period;"* but since he Wrote, the 

 researches of Ramsay, Prestwich, Lyell, Trimmer, Godwin- Austen, 

 J am icson, Falconer, Pengelly, Chambers, and numerous others, in Post- 

 Pliocene geology, render it highly probable thai the "destruction" 

 occurred at a much later period; in short, that Ireland. England, and 

 Spain were united during the earliest age of tin-mining in Cornwall. 



In numerous places on the Irish coast there occur extensive sub- 

 marine peat-bogs, which, it is evident, cannot have been formed when 

 the forests last noticed were growing as supposed, or at the present 



* Mem. Geol. Survey, vol. i. p. IUv 

 VOL. VI. • 2 A 



