202 Dr Buckland on the former Existence of 



to South Georgia in the 54th degree of south latitude, to Kerguelen's 

 Land in the 50th, or to Sandwich Land in the 59th, that the nearest ap- 

 proach to the supposed condition of Scotland during the glacial epoch 

 must be looked for. In those regions the glaciers extend to the sea, and 

 there are no warm valleys into which they can descend and melt, the 

 temperature of summer and winter being also nearly equal. They there- 

 fore probably remain stationary. In the Alps, on the contrary, the inde- 

 finite accumulation of snow is checked, 1st, by evaporation without melt- 

 ing ; 2d, by the descent of glaciers in consequence of gravitation, a cause 

 considered by M. Agassiz not very influential ; 3d, by the descent of gla- 

 ciers arising from the expansion which accompanies the alternate freezing 

 and liquefaction of water. The last, which is the most powerful source 

 of relief in Switzerland, must, Mr Lyell states, be comparatively feeble in 

 countries like South Georgia and Sandwich Land ; and hence that the 

 accumulation of ice can be checked only by evaporation and the gravita- 

 tion of the mass. As the study of the tertiary strata proves that a warm 

 climate certainly preceded the assumed glacier period in the northern 

 hemisphere, and as a milder climate has since prevailed, the author says 

 there are three distinct phases in the action of the supposed ice :• 1st, its 

 gradual coming on ; 2d, its continuance in full intensity ; and 3d, its gra- 

 dual retreat. During the first epoch, Mr Lyell observes, only the higher 

 mountains would send down glaciers to be melted in the plains, as in 

 Switzerland ; and the ice would be in constant motion, the lower boun- 

 daries sometimes advancing, sometimes retrograding ; but that from cen- 

 tury to century it would gradually extend its permanent limits, and 

 would finally reach the sea. During the advance, he says, the terminal 

 moraines would be pushed forward, and forced into the cavities previously 

 occupied by lakes. While the second period continued, he conceives, 

 the snow accumulated to vast thicknesses, filling up the glens and plains, 

 and leaving bare only the peaks and precipices of the loftier mountains ; 

 and that from these points the fragments were detached, and progressively, 

 but almost imperceptibly, conveyed, which are now found at great dis- 

 tances from the parent rock, and at high levels. To the third epoch, or 

 that during which the snows and glaciers gradually disappeared, he as- 

 signs the deposition of the erratic blocks on the hills and in the plains, 

 and the production of the terminal moraines, or the existing transverse 

 mounds, as well as the accumulation of the bodies of water from the 

 melting of the ice, which have in various localities overflowed and modi- 

 fied the outline of the stratified detritus. 



III. On the former Existence of Glaciers in the North of England. 

 By Dr Buckland. 

 In a paper read to the Geological Society on the 2d of December, Dr 

 Buckland noticed, that, proceeding southward from Edinburgh, a large 

 portion of the low lauds is composed of till, or the argillaceous detritus 

 of glaciers, interspersed with pebbles. In the valley of the North Tyne, 



