way of the
descending waters, as in the case of the Mackenzie in North America, and
the Irtish, Obi, Yenesei, Lena, and other rivers of Siberia. (See map,
fig. 1, p. 79.) A partial stoppage of this kind lately occurred (Jan.
31, 1840) in the Vistula, about a mile and a half above the city of
Dantzic, where the river, choked up by packed ice, was made to take a
new course over its right bank, so that it hollowed out in a few days a
deep and broad channel, many leagues in length, through a tract of
sand-hills which were from 40 to 60 feet high.

In Canada, where the winter's cold is intense, in a latitude
corresponding to that of central France, several tributaries of the St.
Lawrence begin to thaw in their upper course, while they remain frozen
over lower down, and thus large slabs of ice are set free and thrown
upon the unbroken sheet of ice below. Then begins what is called the
packing of the drifted fragments; that is to say, one slab is made to
slide over another, until a vast pile is built up, and the whole being
frozen together, is urged onwards by the force of the dammed up waters
and drift-ice. Thus propelled, it not only forces along boulders, but
breaks off from cliffs, which border the rivers, huge pieces of
projecting rock. By this means several buttresses of solid masonry,
which, up to the year 1836, supported a wooden bridge on the St.
Maurice, which falls into the St. Lawrence, near the town of Trois
Rivieres, lat. 46 degrees 20 minutes, were thrown down, and conveyed by
the ice into the main river; and instances have occurred at Montreal of
wharfs and stone-buildings, from 30 to 50 feet square, having been
removed in a similar manner. We learn from Captain Bayfield that anchors
laid down within high-water mark, to secure vessels hauled on shore for
the winter, must be cut out of the ice on the approach of spring, or
they would be carried away. In 1834, the Gulnare's bower-anchor,
weighing half a ton, was transported some yards by the ice, and so
firmly was it fixed, that the force of the moving ice broke a
chain-cable suited for a 10-gun brig, and which had rode the Gulnare
during the heaviest gales in the gulf. Had not this anchor been cut out
of the ice, it would have been earned into deep water and lost.[284]

[Illustration: PLATE II.

BOULDERS DRIFTED BY ICE ON SHORES OF THE ST. LAWRENCE

View taken by Lieut. Bowen, from the N. E., in the Spring of 1835, at
Richelieu Rapid, lat. 46 degrees N.]