if the confluent glaciers are equal in size, or nearer to one
side if unequal.

All sand and fragments of soft stone which fall through fissures and
reach the bottom of the glaciers, or which are interposed between the
glacier and the steep sides of the valley, are pushed along, and ground
down into mud, while the larger and harder fragments have their angles
worn off. At the same time the fundamental and boundary rocks are
smoothed and polished, and often scored with parallel furrows, or with
lines and scratches produced by hard minerals, such as crystals of
quartz, which act like the diamond upon glass.[292] This effect is
perfectly different from that caused by the action of water, or a muddy
torrent forcing along heavy fragments; for when stones are fixed firmly
in the ice, and pushed along by it under great pressure, in straight
lines, they scoop out long rectilinear furrows or grooves parallel to
each other.[293] The discovery of such markings at various heights far
above the surface of the existing glaciers and for miles beyond their
present terminations, affords geological evidence of the former
extension of the ice beyond its present limits in Switzerland and other
countries.

The moraine of the glacier, observes Charpentier, is entirely devoid of
stratification, for there has been no sorting of the materials, as in
the case of sand, mud, and pebbles, when deposited by running water. The
ice transports indifferently, and to the same spots, the heaviest blocks
and the finest particles, mingling all together, and leaving them in one
confused and promiscuous heap wherever it melts.[294]

_Icebergs._--In countries situated in high northern latitudes, like
Spitzbergen, between 70 degrees and 80 degrees N., glaciers, loaded with
mud and rock, descend to the sea, and there huge fragments of them float
off and become icebergs. Scoresby counted 500 of these bergs drifting
along in latitudes 69 degrees and 70 degrees N., which rose above the
surface from the height of 100 to 200 feet, and measured from a few
yards to a mile in circumference.[295] Many of them were loaded with
beds of earth and rock of such thickness, that the weight was
conjectured to be from 50,000 to 100,000 tons. Specimens of the rocks
were obtained, and among them were granite, gneiss, mica-schist,
clay-slate, granular felspar, and greenstone. Such bergs must be of
great magnitude; because the mass of ice below the level of the water is
about eig