402 SPECIAL GEOLOGT. 



the trees retain their natural contour, and the bark, in many 

 of them, is converted into a black carbonaceous substance, 

 whilst the wood is fossilised. Hundreds of tons of this 

 forest are seen stretching far out to sea, at low tides. Vege- 

 table remains are frequently washed out of the cliffs; and 

 bones from the wealden strata, which here form the bed of the 

 British Channel, are cast on this and the adjacent shores. 



OBGANIC REMAINS. The fossil remains of the wealden 

 consist of plants, fresh-water shells, fishes, turtles, ptero- 

 dactyles, colossal reptiles, and birds. The shells are of fresh- 

 water origin, consisting of the genera Cyclas, Unio, and 

 Paludina, with an occasional admixture of marine and 

 estuary species. The reptile remains are chiefly referable to 

 the genera Iguanodon, Hylteosaurus, Plesiosaitrus, Megalo- 

 saurus, Cetiosaurus. The plants are monocotyledonous, con- 

 sisting chiefly of such as are allied to the fern, palm, Yucca, 

 dracsena-draco, and other genera indigenous to the torrid 

 zone, among which Sphenopteris, Clathraria, LoncJiopteris 

 are characteristic. (See fig. 123.) 



SUSSEX MAEBLE. The weald clays contain beds of lime- 

 stone composed of Paludince, a freshwater mollusc, common 

 in rivers and lakes. This substance, when polished, is 

 called Sussex marble, and was used for ornamental purposes 

 by the Romans (fig. 282). During the middle ages it was 

 employed for the decoration of sacred edifices. It forms a 

 row of columns in Chichester cathedral; and in that of 

 Canterbury, the throne is constructed of this rock. A 

 highly interesting proof of its employment by the Romans 

 was afforded, whilst digging the foundation of the present 

 Council-house at Chichester, in 1723 ; the workmen dis- 

 covered a slab of grey Sussex marble, which bore an inscrip- 

 tion of which the following is a translation. 



" The college, or company of artificers, and they who pre- 

 side over sacred rites, or hold offices there, by the authority 

 of King Cogidubnus, the legate of Tiberius Claudius Au- 

 gustus, in Britain, dedicated this temple to Neptune and 

 Minerva, for the welfare of the imperial family ; Pudens, the 

 son of Pudentinus, having given the site." 



FOSSIL PISHES. The strata of the wealden have yielded 

 the scales, rays, teeth, and bones of fishes, allied to the 

 Lepidosteus. These remains usually occur in a fragmentary 



