oe 
down as Martigny. The lake of Distel, on the Saas, those of Rufnen 
and Gurglen, in the Tyrol, and that of Passey, on the Adige, are also 
formed by glaciers. The last has burst its dike six times, with the most 
destructive effects, since 1404. Agassiz traced decided marks of an 
ancient glacier at the north side of Ben Nevis. This glacier, he thinks, 
had closed up the valley of the Spean, and formed a lake in Glenroy, 
in which the banks of gravel} called Parallel Roads, were deposited. 
. The barrier being of ice, which subsequently melted, the absence of 
any marks of its existence is accounted for. At present we shall not 
Stop to inquire whether this theory or Mr. Darwin’s is the more probable, 
Alluvial Deposits.—Agassiz thinks that the floods produced by the 
bursting of such lakes as those described, and by the fusion of the ice, 
tore up the moraines, scattered their materials over the country, and 
formed the unstratified boulder clay, and the stratified sand and gravel 
resting upon it, which now cover nearly the whole surface of the low 
ooumntey. 
_ Ancient extent of Glaciers in Switzerland.—The traces boa ancient 
lateral moraines are seldom very distinct; yet in the lower valleys, 
where no glaciers now exist, in that of the Rhone, for instance, between 
. Martigny and the lake of Geneva, several may be seen ranged in par- 
allel lines, one above another, at 1000, 1200, and even 1500 feet above 
the river. Terminal moraines are found half a mile, a mile, a league, 
and even several leagues from existing glaciers ; but these are in se- 
condary valleys, and belong to the period when the glaciers were re- 
treating into the narrow limits which they now occupy, while the floods 
which occurred at this period had obliterated those of the principal 
valleys. The striated’ and polished surfaces, which had a more dura- 
ble existence, are found at great heights; among other examples, on 
Seideihorn, (an isolated mountain in the Alps, now destitute of glaciers,) 
2590 feet above the bottom of the valley, indicating that ancient gla- 
ciers of this depth or more existed here. The boulders also, or blocs 
és, the creux or pits, and the /apiaz or water-worn gutters, were 
sik observed far beyond the present limits of the glaciers. This first 
Step in the argument conducts Agassiz to the conclusion that the whole 
‘of the Alps, at some ancient period, formed. one vast mer de glace, the 
ice descending to the level of the great Swiss valley which separates 
these mountains from Jura. 
But the same indications of glacial action exist on Mount Jura, which 
Tuns parallel to the Alps, divided from them by the great Swiss valley, 
fifty miles in breadth. This. chain, which is of moderate height, is 
now entirely destitute of glaciers, and, owing to the nature of the rock, 
the marks of abrasion are remarkably numerous and distinet.. They are 
found on the side fronting the Alps from the bottom to the 
