e violence of the wind to the height
of 100 feet, and buried in similar hills of sand.

In Suffolk, in the year 1688, part of Downham was overwhelmed by sands
which had broken loose about 100 years before, from a warren five miles
to the south-west. This sand had, in the course of a century, travelled
five miles, and covered more than 1000 acres of land.[1028] A
considerable tract of cultivated land on the north coast of Cornwall has
been inundated by drift sand, forming hills several hundred feet above
the level of the sea, and composed of comminuted marine shells, in
which some terrestrial shells are enclosed entire. By the shifting of
these sands the ruins of ancient buildings have been discovered; and in
some cases where wells have been bored to a great depth, distinct
strata, separated by a vegetable crust, are visible. In some places, as
at New Quay, large masses have become sufficiently indurated to be used
for architectural purposes. The lapidification, which is still in
progress, appears to be due to oxide of iron held in solution by the
water which percolates the sand.[1029]

_Imbedding of Organic and other Remains in Volcanic Formations on the
Land._

I have in some degree anticipated the subject of this section in former
chapters, when speaking of the buried cities around Naples, and those on
the flanks of Etna (pp. 385. 400.). From the facts referred to, it
appeared that the preservation of human remains and works of art is
frequently due to the descent of floods caused by the copious rains
which accompany eruptions. These aqueous lavas, as they are called in
Campania, flow with great rapidity, and in 1822 surprised and
suffocated, as was stated, seven persons in the villages of St.
Sebastian and Massa, on the flanks of Vesuvius.

In the tuffs, moreover, or solidified mud, deposited by these aqueous
lavas, impressions of leaves and of trees have been observed. Some of
those, formed after the eruption of Vesuvius in 1822, are now preserved
in the museum at Naples.

Lava itself may become indirectly the means of preserving terrestrial
remains, by overflowing beds of ashes, pumice, and ejected matter, which
may have been showered down upon animals and plants, or upon human
remains. Few substances are better non-conductors of heat than volcanic
dust and scoriae, so that a bed of such materials is rarely melted by a
superimposed lava-current. After consolidation, the lava affords secure
protection to the