The most salient and characteristic feature of this age is, undoubtedly,
the appearance of animals belonging to the class of Mammals. But the
organisation, quite special, of the first of the Mammalia will certainly
be a matter of astonishment to the reader, and must satisfy him that
Nature proceeded in the creation of animals by successive steps, by
transitions which, in an almost imperceptible manner, connect the beings
of one age with others more complicated in their organisation. The first
Mammals which appeared upon the earth, for example, did not enjoy all
the organic attributes belonging to the more recent creations of the
class. In the latter the young are brought forth living, and not from
eggs, like Birds, Reptiles, and Fishes. But the former belonged to that
order of animals quite special, and never numerous, the young of which
are transferred in a half-developed state, from the body of the mother
to an external pouch in which they remain until they become perfected;
in short, to marsupial animals. The mother nurses her young during a
certain time in a sort of pouch external to the body, in the
neighbourhood of the abdomen, and provided with teats to which the young
adhere. After a more or less prolonged sojourn in this pouch, the young
animal, when sufficiently matured and strong enough to battle with the
world, emerges from its warm retreat, and enters fully into life and
light; the process being a sort of middle course between oviparous
generation, in which the animals are hatched from eggs after exclusion
from the mother’s body, like Birds; and viviparous, in which the animals
are brought forth alive, as in the ordinary Mammals.
[Illustration: Fig. 109.--General view of the succession of British
strata, with the elevations they reach above the level of the sea.
_G_, Granitic rocks; _a_, Gneiss; _b_, Mica-schist; _c_, Skiddaw or
Cumbrian Slates; _d_, Snowdon rocks; _e_, Plynlymmon rocks; _f_,
Silurian rocks; _g_, Old Red Sandstone; _h_, Carboniferous Limestone;
_i_, Millstone Grit; _k_, Coal-measures; _l_, Magnesian Limestone; _m_,
New Red Sandstone; _n_, Lias; _o_, Lower, Middle, and Upper Oolites;
_p_, Greensand; _q_, Chalk; _r_, Tertiary strata.]
In standard works on natural history the animals under consideration are
classed as _mammiferous Didelphæ_. They are brought forth in an
imperfect state, and during their transitional condition are suckled in
a pouch supported by bones called _marsupial_, which are attached by
their extremities to the pelvis, and serve to support the marsupium,
whence the animals provided with these provisions for bringing up their
progeny are called _Marsupial Mammals_. The Opossum, Kangaroo, and
Ornithorhynchus are existing representatives of this group.
[Illustration: Fig. 110.--Jaw of Thylacotherium Prevostii.]
[Illustration: Fig. 111.--Jaw of Phascolotherium.]
The name of _Thylacotherium_, or _Amphitherium_, or _Phascolotherium_,
is given to the first of these marsupial Mammals which made their
appearance, whose remains have been discovered in the Lower Oolite, and
in one of its higher stages, namely, that called the _Great Oolite_.
Fig. 110 represents the jaw of the first of these animals, and Fig. 111
the other--both of the natural size. These jaw-bones represent all that
has been found belonging to these early marsupial animals; and Baron
Cuvier and Professor Owen have both decided as to their origin. The
first was found in the Stonesfield quarries. The Phascolotherium, also a
Stonesfield fossil, was the ornament of Mr. Broderip’s collection. The
animals which lived on the land during the Lower Oolitic period would be
nearly the same with those of the Liassic. The insects were, perhaps,
more numerous.
The marine fauna included Reptiles, Fishes, Molluscs, and Zoophytes.
Among the first were the Pterodactyle, and a great Saurian, the
Teleosaurus, belonging to a family which made its appearance in this
age, and which reappears in the following epoch. Among the Fishes, the
Ganoids and Ophiopsis predominate. Among the Ammonites, _Ammonites
Humphriesianus_, _A. Herveyii_ (Fig. 112), _A. Brongniarti_, _Nautilus
lineatus_, and many other representatives of the cephalopodous Mollusca.
Among the Brachiopods are _Terebratula digona_ (Fig. 113) and _T.
spinosa_. Among the Gasteropoda the _Pleurotomaria conoidea_ is
remarkable from its elegant shape and markings, and very unlike any of
the living _Pleurotoma_ as represented by _P. Babylonia_ (Fig. 114).
_Ostrea Marshii_ and _Lima proboscidea_, which belong to the Acephala,
are fossil Mollusca of this epoch, to which also belong _Entalophora
cellarioides_, _Eschara Ranviliana_, _Bidiastopora cervicornis_; elegant
and characteristic molluscous Polyzoa. We give a representation of two
living species, as exhibiting the form of these curious beings. (Figs.
115 and 116.)
[Illustration: Fig. 112.--Ammonites Herveyii.]
[Illustration: Fig. 113.--Terebratula digona.]
[Illustration: Fig. 114.--Pleurotoma Babylonia. (Recent.)]
The Echinoderms and Polyps appear in great numbers in the deposits of
the Lower Oolite: _Apiocrinus elegans_, _Hyboclypus gibberulus_,
_Dysaster Endesii_ represent the first; _Montlivaltia caryophyllata_,
_Anabacia orbulites_, _Cryptocœnia bacciformis_, and _Eunomia radiata_
represent the second.
[Illustration: Fig. 115.--Adeona folifera.
(Recent Polyzoa.)]
[Illustration: Fig. 116.--Cellaria loriculata.
(Recent Polyzoa.)]
This last and most remarkable species of Zoophyte presents itself in
great masses many yards in circumference, and necessitates a long period
of time for its production. This assemblage of little creatures living
under the waters but only at a small depth beneath the surface, as Mr.
Darwin has demonstrated, has nevertheless produced banks, or rather
islets, of considerable extent, which at one time constituted veritable
reefs rising out of the ocean. These reefs were principally constructed
in the Jurassic period, and their extreme abundance is one of the
characteristics of this geological age. The same phenomenon continues in
our day, but by the agency of a new race of zoophytes, which carry on
their operations, preparing a new continent, probably, in the _atolls_
of the Pacific Ocean. (See Fig. 108, p. 240.)
[Illustration: Fig. 117.
1, Otopteris dubia; 2, Otopteris obtusa; 3,
Otopteris acuminata; 4, Otopteris cuneata.]
The flora of the epoch was very rich. The Ferns continue to exist, but
their size and bearing were sensibly inferior to what they had been in
the preceding period. Among them Otopteris, distinguished for its
simply pinnated leaves, whose leaflets are auriculate at the base: of
the five species, 1, _O. dubia_; and 2, _O. obtusa_; and 3, _O.
acuminata_; and 4, _O. cuneata_ (Fig. 117), are from the Oolite. In
addition to these we may name _Coniopteris Murrayana_, _Pecopteris
Desnoyersii, Pachypteris lanceolata_, and _Phlebopteris Phillipsii_; and
among the Lycopods, _Lycopodus falcatus_.
The vegetation of this epoch has a peculiar facies, from the presence of
the family of the Pandanaceæ, or screw-pines, so remarkable for their
aërial roots, and for the magnificent tuft of leaves which terminates
their branches. Neither the leaves nor the roots of these plants have,
however, been found in the fossil state, but we possess specimens of
their large and spherical fruit, which leave no room for doubt as to the
nature of the entire plant.
The Cycads were still represented by the _Zamias_, and by many species
of Pterophyllum. The Conifers, that grand family of recent times, to
which the pines, firs, and other trees of our northern forests belong,
began to occupy an important part in the world’s vegetation from this
epoch. The earliest Conifers belonged to the genera _Thuites_,
_Taxites_, and _Brachyphyllum_. The _Thuites_ were true _Thuyas_,
evergreen trees of the present epoch, with compressed branches, small
imbricated and serrated leaves, somewhat resembling those of the
Cypress, but distinguished by many points of special organisation. The
_Taxites_ have been referred, with some doubts, to the Yews. Finally,
the _Brachyphyllum_ were trees which, according to the characteristics
of their vegetation, seem to have approached nearly to two existing
genera, the _Arthotaxis_ of Tasmania, and the _Weddringtonias_ of South
Africa. The leaves of the Brachyphyllum are short and fleshy, with a
large and rhomboidal base.