of lime. The surface generally, both under the incrustation, and where
freed from it, was of a variegated color, mottled with spots of green,
dirty white, and red. On minute inspection with a lens, the green and
red patches proved to consist of crystals of the red oxide and carbonate
of copper, and the dirty white chiefly of oxide of tin.

The mineralizing process, says Dr. Davy, which has produced these new
combinations, has, in general, penetrated very little into the substance
of the helmet. The incrustation and rust removed, the metal is found
bright beneath; in some places considerably corroded, in others very
slightly. It proves, on analysis, to be copper, alloyed with 18.5 per
cent. of tin. Its color is that of our common brass, and it possesses a
considerable degree of flexibility.

"It is a curious question," he adds, "how the crystals were formed in
the helmet, and on the adhering calcareous deposit. There being no
reason to suppose deposition from solution, are we not under the
necessity of inferring, that the mineralizing process depends on a small
motion and separation of the particles of the original compound? This
motion may have been due to the operation of electro-chemical powers
which may have separated the different metals of the alloy.[1093]

_Effects of the Subsidence of Land, in imbedding Cities and Forests in
subaqueous Strata._

We have hitherto considered the transportation of plants and animals
from the land by _aqueous_ agents, and their inhumation in lacustrine or
submarine deposits, and we may now inquire what tendency the subsidence
of tracts of land may have to produce analogous effects. Several
examples of the sinking down of buildings, and portions of towns near
the shore, to various depths beneath the level of the sea during
subterranean movements, were before enumerated in treating of the
changes brought about by _inorganic_ causes. The events alluded to were
comprised within a brief portion of the historical period, and confined
to a small number of the regions of active volcanoes. Yet these
authentic facts, relating merely to the last century and a half, gave
indications of considerable changes in the physical geography of the
globe, and we are not to suppose that these were the only spots
throughout the surrounding land and sea which suffered similar
depressions.

If, during the short period since South America has been colonized by
Europeans, we have proof of alterations of