Of the perfect transmutation into flint of the most delicate organic structures, the pebbles strewn along the sea-shore of the south coast of England, afford a beautiful illustration; those from the Isle of Wight are especially celebrated for their rich and varied colours. The most common and interesting are those which exhibit sections of Choanites, as in the specimen which suggested the reflections embodied in these pages. Other allied forms are scarcely less beautiful; the petrified zoophytes called _Siphonia_, which, when living, consisted of a soft mass traversed by tubes, for the free ingress and egress of the water, often display the internal structure of the original: as in the polished transverse section figured above, _Lign. 24, fig. 3_. Other bodies of this class occur in the flint, and present interesting examples of the zoophytes of the chalk ocean. But many of the Isle of Wight pebbles exhibit no traces of animal structure, yet are valuable and instructive as mineralogical specimens: such are the clear and transparent pebbles with bands and veins of quartz and chalcedony. Some specimens are as pellucid as rock-crystal; others are of a bright yellow, amber, dark-brown, and bluish-black colour, and are often mottled with dendritical or arborescent manganese. (_Plate IV._) The moss agates, as they are called by the lapidaries, are silicified sponges. Small pebbles of pure transparent rock-crystal are often found among the shingle in Compton and Sandown bays, and have probably been washed out of the wealden strata; for similar stones occur in the Tilgate grit, and at Tunbridge Wells: in the latter place, they are cut and polished for rings, brooches, &c. [Illustration: _Plate IV._ _Polished sections of Pebbles._ _Page 86._] [Sidenote: ZOOPHYTES OF THE CHALK.] On the shores of the Isle of Wight, pebbles of jasper, resembling those from Egypt, and of banded quartz, with arborescent markings, or with zones of rich brown, are also met with; these do not appear to have originated from the chalk strata. Pebbles of silicified wood have been collected in Sandown bay by Mr. Fowlstone; and water-worn boulders and pebbles of petrified wood, bones, &c., are common in Brook bay; rolled masses of the fresh-water shelly limestones (Sussex and Purbeck marbles) are also abundant in the same localities.[AO] [AO] All these varieties may be obtained of Mr. Fowlstone, 4, Victoria Arcade, Ryde. Note VIII. Page 45. _Zoophytes of the Chalk._ Zoophytes, especially sponges, occur in such prodigious numbers in some of the chalk strata, that the nucleus of almost every flint nodule is an organic body. In many instances the silex has completely permeated the animal substance, as in the pebbles before described; but sometimes the sponge is a white calcareous mass, occupying a hollow in the flint: a branched specimen of this kind, exposed on breaking a small nodule, is represented at _Lign. 24, fig. 2_.