arine
races. The phenomena attending their inhumation in lacustrine deposits
are sometimes revealed to our observation by the drainage of small
lakes, such as are those in Scotland, which have been laid dry for the
sake of obtaining shell marl for agricultural uses.

In these recent formations, as seen in Forfarshire, two or three beds of
calcareous marl are sometimes observed separated from each other by
layers of drift peat, sand, or fissile clay. The marl often consists
almost entirely of an aggregate of shells of the genera Limnea,
Planorbis, Valvata, and Cyclas, of species now existing in Scotland. A
considerable proportion of the Testacea appear to have died very young,
and few of the shells are of a size which indicates their having
attained a state of maturity. The shells are sometimes entirely
decomposed, forming a pulverulent marl; sometimes in a state of good
preservation. They are frequently intermixed with stems of Charae and
other aquatic vegetables, the whole being matted together and
compressed, forming laminae often as thin as paper.

_Fossilized seed-vessels and stems of Chara._--As the Chara is an
aquatic plant which occurs frequently fossil in formations of different
eras, and is often of much importance to the geologist in characterizing
entire groups of strata, I shall describe the manner in which I have
found the recent species in a petrified state. They occur in a marl-lake
in Forfarshire, inclosed in nodules, and sometimes in a continuous
stratum of a kind of travertin.

[Illustration: Fig. 102.

Seed-vessel of Chara hispida.

_a_, Part of the stem with the seed-vessel attached. Magnified.

_b_, Natural size of the seed vessel.

_c_, Integument of the Gyrogonite, or petrified seed-vessel
of _Chara hispida_, found in the Scotch marl-lakes.
Magnified.

_d_, Section showing the nut within the integument.

_e_, Lower end of the integument to which the stem was attached.

_f_, Upper end of the integument to which the stigmata were attached.

_g_, One of the spiral valves of _c_.

]

The seed-vessel of these plants is remarkably tough and hard, and
consists of a membranous nut covered by an integument (_d_, fig. 102.)
both of which are spirally striated or ribbed. The integument is
composed of five spiral valves, of a quadrangular form (_g_). In _Chara
hispida_, which abounds in the lakes of Forfarshire, and which has
become fossil in the Bakie Loch,