Fig. 1. A flint from the gravel-pits at Hackney. Its form is derived from the enclosed zoophyte, part of whose structure is exposed in the upper portion of the figure. This fossil zoophyte (_Choanites Königi_, of Mantell) is very abundant in some of the chalk strata, and many of the most beautifully marked pebbles cut and polished for brooches by the lapidaries of Brighton, Bognor, and the Isle of Wight, are the silicified soft parts of this animal. The original was of a subglobular form, and probably of a soft fleshy consistence; it had a deep central cavity, whence numerous tubes diverged, and ramified throughout the mass; it was fixed at the base by radicle or root-like processes.[32] [Footnote 32: See Medals of Creation, p. 264. "Thoughts on a Pebble," (eighth edition,) contains coloured figures and a full description of these fossils.] Fig. 2. This is another characteristic and abundant fossil zoophyte of the chalk and flint. The specimen figured is a water-worn pebble, and therefore gives but obscure indications of the form and structure of the original. The fungiform flints--called in Sussex petrified mushrooms--belong to the same genus (_Ventriculites_, of Mantell): and highly interesting specimens occur in which some part of the zoophyte is invested with flint, and the other part expanded in the chalk. The original was probably a polyparium--that is, the skeleton or support of an aggregation of coral-polypes--of a funnel shape, the polype-shells being situated on the inner surface: the base was attached by root-like fibres.[33] The polype-cells are cylindrical and regular, and clusters of beautiful casts of them often occur on flints. [Footnote 33: Consult Medals of Creation, pp. 270-279: and Wonders of Geology, sixth edition, p. 638.] Fig. 3. This specimen is described by Mr. Parkinson as "a pear-shaped alcyonite from Switzerland." It is probably one of those fossil zoophytes allied to the sponges (called _Siphonia_), in which the upper part is of a bulbous or pear-like form, and is supported by a stem with root-like processes at the base. The bulb has a central cavity studded with irregular pores, that communicates with the parallel longitudinal tubes of which the stem is composed: a structure admitting of that ready ingress and egress of the sea-water, which this class of organisms requires. There are numerous species in the greensand of the chalk formation.[34] [Footnote 34: Medals of Creation, p. 258, Lign. 56.] Fig. 4. A variety of Siphonia (_Jerea excavata_, of Michelin), from the greensand of Wiltshire. Fig. 5. A silicified Siphonia from Saumur.