Sir Roderick Murchison has shown that in Russia, when the Dwina is at
its maximum height, and penetrates into the chinks of its limestone
banks, when frozen and expanded it causes disruptions of the rock,
the entanglement of stony fragments in the ice. In remarkable spring
floods, the stream so expands that in bursting it throws up its icy
fragments to 15 or 20 feet above the stream; and the waters subsiding,
these lateral ice-heaps melt away, and leave upon the bank the
rifled and angular blocks as evidence of the highest ice-mark. In
Lapland, M. Böhtlingk assures us that he has found _large granitic
boulders weighing several tons actually entangled and suspended, like
birds’-nests, in the branches of pine-trees, at heights of 30 or 40
feet above the summer level of the stream_![28]