GLACIEE TABLES. 
On the surface of the Glaciers, or streams of ice which fill the upper 
valleys of Alpine districts, may frequently he noticed enormous hlocks 
or slahs of stone perched upon stems of ice like huge mushrooms ; 
sometimes entirely, and at other times partly, supported in the air. 
They are called Glacier Tables. One of them, noticed hy Mr. Forbes, 
consisted of a flat block of granite measuring twenty-three feet by seven- 
teen feet, and about three and a half feet in thickness. In the month 
of June 1842 it was easy to step upon this stone from the general sur- 
face of the glacier ; but as the season advanced it changed its appearance 
remarkably. The waste of ice at the surface caused the glacier to sink 
all round the stone, while the ice immediately beneath it was protected 
from the sun and rain, as by an umbrella. The stone thus appeared to 
rise above the level of the glacier, supported on an elegant pedestal of 
beautifully veined ice. " Each time I visited it," says Mr. Forbes, " it 
was more difficult of ascent ; and at last, on the 6th August, the pillar 
of ice was thirteen feet high, and the broad stone so delicately poised on 
the summit of it (which measured but a few feet in any direction), that 
it was almost impossible to guess on what it would ultimately fall, al- 
though, by the process of the thaw, its fall in the course of the summer 
was certain." On a still later day, when Mr. Forbes made a sketch of it, 
" it was," he says, "probably the most beautiful object of the kind to 
be seen anywhere in Switzerland. The ice of the pedestal presented the 
beautiful lamellar structure parallel to the length of the glacier. During 
my absence in the end of August, it slipped from its support ; and in 
the month of September it was beginning to rise upon a new one, whilst 
the unmelted base of the first was still very visible upon the glacier." 
Glacier tables are formed only of such thick blocks of stone as will 
prevent the heat of the sun from penetrating through. If the slabs are 
thin, and of a dark colour, a contrary effect is produced; instead of 
rising, they sink. The heat of the sun is absorbed so quickly that it 
melts the ice beneath, and the stone soon disappears. A leaf wafted by 
the wind upon the glacier, a dead insect, or a few grains of black sand, 
will all sink ; while blocks of stone as large as a house, and weighing 
millions of pounds, are thrust up into the air. 
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