they have been subjected to concretionary action,
as is observable to such a marked extent in the Permian limestones.
Nevertheless, much interest is attached to the organic remains,
as marking a kind of transition-period between the Palaeozoic
and Mesozoic epochs.

[Illustration: Fig. 134.--_Walchia piniformis_, from the Permian
of Saxony, a, Branch; b, Twig, (After Gutbier.)]

The _plants_ of the Permian period, as a whole, have a distinctly
Palaeozoic aspect, and are far more nearly allied to those of the
Coal-measures than they are to those of the earlier Secondary
rocks; though the Permian _species_ are mostly distinct from
the Carboniferous, and there are some new genera. Thus, we find
species of _Lepidodendron, Calamites, Equisetites, Asterophyllites,
Annularia_, and other highly characteristic Carboniferous genera.
On the other hand, the _Sigillariods_ of the Coal seem to have
finally disappeared at the close of the Carboniferous period. Ferns
are abundant in the Permian rocks, and belong for the most part to
the well-known Carboniferous genera _Alethopteris, Neuropteris,
Sphenopteris_, and _Pecopteris_. There are also Tree-ferns referable
to the ancient genus _Psaronius_. The _Conifers_ of the Permian
period are numerous, and belong in part to Carboniferous genera.
A characteristic genus, however, is _Walchia_ (fig. 134),
distinguished by its lax short leaves. This genus, though not
exclusively Permian, is mainly so, the best-known species being
the _W. Piniformis_. Here, also, we meet with Conifers which
produce true cones, and which differ, therefore, in an important
degree from the Taxoid Conifers of the Coal-measures. Besides
_Walchia_, a characteristic form of these is the _Ullmania
selaginoides_, which occurs in the Magnesian Limestone of Durham,
the Middle Permian of Westmorland, and the "Kupfer-schiefer" of
Germany. The group of the _Cycads_, which we shall subsequently
find to be so characteristic of the vegetation of the Secondary
period, is, on the other hand, only doubtfully represented in
the Permian deposits by the singular genus _Noeggerathia_.

The _Protozoans_ of the Permian rocks are few in number, and
for the most part imperfectly known. A few _Foraminifera_ have
been obtained from the Magnesian Limestone of England, and the
same formation has yielded some ill-understood Sponges. It does
not seem, however, altogether impossible that some of the singular
"concretions" of this formation may