[Illustration: XXIII.--Ideal Landscape of the Eocene Period.] The hitherto unknown forms of _Schizaster_ are remarkable among Echinoderms; the Zoophytes are also abundant, especially the _Foraminifera_, which seem to make up by their numbers for their deficiency in size. It was in this period, in the bosom of its seas, and far from shore, that the _Nummulites_ existed, whose calcareous envelopes play such a considerable part as the elements of some of the Tertiary formations. The shelly agglomerates of these Protozoan Rhizopods constitute now very important rocks. The Nummulitic limestone forms, in the chain of the Pyrenees, entire mountains of great height; in Egypt it forms strata of considerable extent, and it is of these rocks that the ancient pyramids were built. What an enormous time must have been necessary to convert the remains of these little shells into beds many hundreds of feet thick! The _Miliola_ were also so abundant in the Eocene seas as to constitute the greater part of calcareous rocks[83] out of which Paris has been built. Agglomerated in this manner, these little shells form the continuous beds of limestone which are quarried for building purposes in the environs of Paris, at Gentilly, Vaugirard, and Châtillon. [83] Similar beds of Miliolite limestone are found in the Middle Bagshot beds on the coast of Sussex, off Selsey--the only instance in England of the occurrence of such calcareous deposits of Middle Eocene age.--H. W. B. * * * * * On the opposite page we present, in PLATE XXIII., an imaginary landscape of the Eocene period. We remark amongst its vegetation a mixture of fossil species with others belonging to the present time. The Alders, the Wych-elms, and the Cypresses, mingle with _Flabellaria_; the Palms of extinct species. A great Bird--a wader, the _Tantalus_--occupies the projecting point of a rock on the right; the Turtle (_Trionyx_), floats on the river, in the midst of Nymphæas, Nenuphars, and other aquatic plants; whilst a herd of Palæotheria, Anoplotheria, and Xiphodon peacefully browse the grass of the natural meadows of this peaceful oasis.