€ Prof. Pictet on the Ice-caves of the Jura and the Alps. 
face of the ice, is about £7 feet ; and the thickness of the bed 
of compact calcareous rock, which forms this enormous vault, 
is about 18 inches in thickness only. 
The length of the icy surface, that is, almost the whole length 
of the grotto, is 75 feet,. and the mean width 40 feet, which gives 
for the total of the workable Surface 75x40— 8000 square feet, 
and as many cubic feet for each layer of ice of a foot thick, 
which is carried away. A French cubic foot of pure ice weighs 
about 65 lb. marc weight, which gives, for the supposed depth 
of a foot, carried away from the whole extent of the grotto, 
3000 x 65 = 195,000 lb., making 1950 quintals of ice, which 
would load 68 waggons, carrying 25 quintals each. 
The working of the ice is the same as that of a quarry : it is 
cut with appropriate tools into long wedges, and divided by 
transverse cuts about a foot distant from each other, and suffi- 
ciently deep to enable them easily to detach blocks of a cubic 
foot. They work for two or three hours in preparing a certain 
quantity of them, which they then carry one by one in hods, to 
a magazine near the place where the waggons are loaded. 
The part of the grotto to the left, and\vhich is more particular- 
ly under the ellipsoidal vault, already mentioned, yises against 
the lower part of this vault, with a very rapid slope. The part 
to the right, the roof of which is very irregular, is occupied by 
. the workable ice ; and the natural wall which bounds it to the 
right, is almost vertical. 
There are at the extremity of the grotto, at a certain height 
against its partitions, stalactites, which one would take at the first 
view for carbonate of lime, but which are ice of an opaque 
white. They are formed against the inclined partitions of the 
grotto, by the filtering of a small current of water, which is vi- 
sible towards' the extremity of the grotto to the right, between 
the ice and the almost vertical partition of rock which encloses 
it ; and there it falls into a very deep hole. It is to be presumed 
that all this depth is filled up by the mass of ice which was un- 
der our feet. 
The thermometer which, suspended in the open air and in 
the shade, at the outside of the grotto, stood at 63° of Fahr., 
when placed in the middle: of the grotto, 2 feet above the 
