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POPULAR SCIENCE REVIEW. 
perfection than among the Mont Blanc Alps around Chamounix. 
I visited this district during the autumn of 1875. Here the 
changes are most marked within the last thirty years. Sir Wm. 
Guise pointed out to me the spot where the foot of the glacier 
of the Mer de Glace then extended beyond the Arveiron’s source. 
It has retreated nearly a hundred yards. Higher up, near the 
Montanvert, the glacier has sunk twenty feet below the rock 
from which he, thirty years ago, stepped upon the ice. Such has 
been the gradual diminution within that period. The older 
guides confirm Sir William’s statement, and the correctness of 
his observations. Here all around we may study moraines far 
from the glacier, roches moutonees of gneiss, worn and polished 
as if the ice had vanished suddenly the day before, and bare 
and brown as if scathed by fire ; with here and there a bloc 
perche of white granite which has travelled from Mont Blanc. 
Near the source of the Arveiron the Mer de Glace has piled 
up a great terminal moraine, rising into a long low hill, one 
side of which is covered with trees. This hill is made up of 
masses of rock of all sizes, which once were wanderers upon the 
slow moving glacier when it thrust its ice foot beyond the 
present termination. One great erratic of Mont Blanc granite 
has been marked with a large red 2, by the Geological Society 
of Switzerland, to prevent its being blasted by gunpowder for 
building purposes. This erratic is as large as a good-sized 
cottage, and is an example of the size of the rock masses which 
now and then fall from the hills above the glacier, and are 
carried forward often for many miles upon the ice. Numerous 
bloc perches are stranded on the flanks of the hills on the right 
bank of the Mer de Glace, as you descend from the Jardin to the 
Chapeau, which the observer may at once see do not belong to 
the rocks on which they lie stranded. There are some rock 
masses, too, which have been derived from different localities,, 
now perched on the ice towards the foot of the glacier where it 
comes down into the valley among chalets, and pine woods, and 
Alpine gardens. 
Such are some of the modern phenomena the geologist learns 
to observe among glaciers and ice action. These, however, are 
merely subsidiary to the interest with which we pursue the 
examination of the evidence that there were, in former days, 
glaciers of colossal dimensions , which filled the great vales of 
Switzerland with ice, and which reached from the Alps to the 
Jura, across where is now the Lake of Geneva. To this 
strange history belongs the transportation of the celebrated 
Mont Blanc granite boulders, which are stranded 900 feet above 
the Lake of Neufchatel, and of which the Pierra a Bot is the 
most remarkable. Again, on the east of the Lake of Geneva, 
opposite Bex, are the great blocs perches of Month ey, which lie 
