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spect to the geological age of the beds containing the marine shells, 
Mr. Lyell. is of opinion that it is synchronous with that of the 
older of the recent formations on the Clyde, examined by Mr. Smith 
of Jordan Hill, and Mr. E. Forbes; and with respect to the age of 
the till and stratified gravel last formed, he is of opmion that it is 
very modern, because these accumulations constitute exclusively the 
dams of certain marl-lochs to the very bottom of the sediment 
formed, in which al the Testacea and skeletons of quadrupeds, as 
well as the remains of plants which have been found, are of existing 
species. 
The third district, or that of the Sidlaw Hills, claimed Mr. Lyell’s 
attention more particularly on account of the Grampian boulders 
with which it abounds. This range, whose greatest height is 1500 
feet above the sea, is composed of anticlinal strata of grey sandstone, 
belonging to the old red sandstone, with associated trap. It is co- 
vered, as well as the whole of the country between Strathmore and 
the Tay, with the impervious till, containing Grampian boulders and 
fragments of the subjacent grey sandstone. ‘The finest instances of 
erratics observed by Mr. Lyell occur on Pitscanly Hill, 700 feet, and 
the adjacent hill of Turin, 800 feet above the level of the sea. About 
forty feet below the summit, on the southern side of the former, is 
a block of mica-slate thirteen feet long, seven broad, and seven in 
height above the ground, Four smaller and equally angular masses, 
from three to six feet in diameter, he close to its north end, as if se- 
vered from it. One of the nearest pomts at which this gneiss occurs 
im situ, is the Craig of Balloch, fifteen miles distant, on the northern 
extremity of the Creigh Hill, and between these points intervenes 
the great valley of Strathmore and the hills of Finhaven, Other 
Grampian boulders, from three to six feet in diameter, occur on the 
hills between Lumley Den and Lundie, at the height of 1000 feet ; 
and Mr. Blackadder has found fragments of mica-schist one foot in 
diameter on the summit of Craigowl, the highest point of the Sid- 
law Hills, and exceeding 1500 feet above the level of the sea. 
In conclusion, Mr. Lyell offers some remarks on the conditions 
under which glaciers may have existed in Scotland, and the differ- 
ences between them and those of the glaciers of Switzerland. He 
states that the glaciers of the latter country being situated 11° 
further to the south, they can present but an imperfect analogy with 
permanent masses of ice in Forfarshire, and that it is to South 
Georgia, Kergulen’s Land and Sandwich Land that we must look for 
the nearest approach to that state of things which must have existed 
in Scotland during the glacial epoch. In those regions of the south- 
ern hemisphere the ice reaches to the borders of the sea, and the 
temperature of summer and winter being nearly equalized, the gla- 
ciers probably remain almost stationary, like those of the Alps in 
winter, and can be diminished by only the first two of the three 
causes which tend to check an indefinite accumulation of snow in 
Switzerland ; viz. 1st, evaporation without melting ; and 2ndly, the 
descent of glaciers by gravitation, considered by M. Agassiz to be 
not very influential :—the third cause, the descent of glaciers arising 
