ers as Quenstedt,
Oppel, D'Orbigny, Wright, De la Beche, Tate, and others, the
entire series of Jurassic sediments admits of a more complete
and more elaborate subdivision into zones characterised by special
life-forms than has as yet been found practicable in the case
of any other rock-series.

[Illustration: Fig. 159. GENERALIZED SECTION OF THE JURASSIC ROCKS
OF ENGLAND.]

[Illustration: Fig. 160.--_Mantellia_ (_Cycadeoidea_) _megalophylla_,
a Cycad from the Purbeck "dirt-bed." Upper Oolites, England.]

The _plants_ of the Jurassic period consist principally of Ferns,
Cycads, and Conifers--agreeing in this respect, therefore, with
those of the preceding Triassic formation. The _Ferns_ are very
abundant, and belong partly to old and partly to new genera. The
_Cycads_ are also very abundant, and, on the whole, constitute the
most marked feature of the Jurassic vegetation, many genera of this
group being known (_Pterophyllum, Otozamites, Zamites, Crossozamia,
Williamsonia, Bucklandia,_ &c.) The so-called "dirt-bed" of the
Purbeck series consists of an ancient soil, in which stand erect
the trunks of Conifers and the silicified stools of Cycads of
the genus _Mantellia_ (fig.160). The _Coniferoe_ of the Jurassic
are represented by various forms more or less nearly allied to
the existing _Araucarioe_; and these are known not only by their
stems or branches, but also in some cases by their cones. We
meet, also, with the remains of undoubted Endogenous plants,
the most important of which are the fruits of forms allied to
the existing Screw-pines (_Pandaneoe_), such as _Podocarya_ and
_Kaidacarpum_. So far, however, no remains of Palms have been
found; nor are we acquainted with any Jurassic plants which could
be certainly referred to the great "Angiospermous" group of the
Exogens, including the majority of our ordinary plants and trees.

Amongst animals, the _Protozoans_ are well represented in the
Jurassic deposits by numerous _Foraminifers_ and _Sponges_; as
are the _Coelenterates_ by numerous _Corals_. Remains of these
last-mentioned organisms are extremely abundant in some of the
limestones of the formation, such as the "Coral-rag" and the
Great Oolite; and the former of these may fairly be considered
as an ancient "reef." The _Rugose Corals_ have not hitherto been
detected in the Jurassic rocks; and the "_Tabulate Corals_,"
so-called, are represented only by examples of the modern genus
_Millepora_. With this exce