SNOW AND ICE. 
125 
glacier advances so far on account of the magnitude 
of the snow-fields above. In 1 8 1 8 the lower Grindel- 
wald glacier descended to 983 metres above the sea 
level. In 1870, it had receded to 1080 metres. 
The lower limit of the Mer de Glace is 1120 metres. 
In the Eastern Alps, where the climate is more con- 
tinental and drier, the general limit is from 1800 to 
2300 metres.. 
Ice Tables. 
Small bodies, such as pebbles, dust, insects, etc., 
tend to sink into the ice. On the other hand larger 
stones intercept the heat. 
On most glaciers may be seen large stones rest- 
ing on pillars of ice. These are the so-called Ice 
tables. If the stone be wide and flat, the pillar may 
reach a considerable height, for the ice immediately 
under it, being protected from the rays of the sun, 
melts less rapidly. The tables are rarely horizontal, 
but lean to the south, that side being more exposed 
to the sun. Small stones and sand, on the contrary, 
absorb the heat and melt the snow beneath them, 
unless indeed there is a sufficient thickness of sand, 
in which case they intercept the heat and form 
cones, sometimes ten or even twenty feet in height. 
Medial moraines in the same way tend to check 
