the sea, are
phenomena common to almost every delta.

The variety of species of Testacea contained in the recent calcareous
marl of Scotland, before mentioned, is very small, but the abundance of
individuals extremely great, a circumstance very characteristic of
freshwater formations in general, as compared to marine; for in the
latter, as is seen on sea-beaches, coral-reefs, or in the bottom of the
seas examined by dredging, wherever the individual shells are
exceedingly numerous, there rarely fails to be a vast variety of
species.

_Imbedding of the Remains of Marine Plants and Animals._

_Marine plants._--The large banks of drift sea-weed which occur on each
side of the equator in the Atlantic, Pacific, and Indian oceans, were
before alluded to.[1105] These, when they subside, may often produce
considerable beds of vegetable matter. In Holland, submarine peat is
derived from Fuci, and on parts of our own coast from _Zostera marina_.
In places where Algae do not generate peat, they may nevertheless leave
traces of their form imprinted on argillaceous and calcareous mud, as
they are usually very tough in their texture.

Sea-weeds are often cast up in such abundance on our shores during heavy
gales, that we cannot doubt that occasionally vast numbers of them are
imbedded in littoral deposits now in progress. We learn from the
researches of Dr. Forchhammer, that besides supplying in common with
land plants the materials of coal, the Algae must give rise to important
chemical changes in the composition of strata in which they are
imbedded. These plants always contain sulphuric acid, and sometimes in
as large a quantity as 8-1/2 per cent., combined with potash: magnesia
also and phosphoric acid are constant ingredients. Whenever large masses
of sea-weeds putrefy in contact with ferruginous clay, sulphuret of
iron, or iron pyrites, is formed by the union of the sulphur of the
plants with the iron of the clay; while the potash, released from its
union with the clay (_i. e._ silicate of alumina), forms with it a
peculiar compound. Many of the mineral characteristics of ancient rocks,
especially the alum slates, and the pyrites which occur in clay slate,
and the fragments of anthracite in marine Silurian strata, may be
explained by the decomposition of fucoids or sea-weeds.[1106]

_Imbedding of cetacea._--It is not uncommon for the larger Cetacea,
which can float only in a considerable depth of water, to be carried
dur