CONCLUDING OBSERVATIONS. 299 



resemble a species of Tellina, or ISTucula, and others are supposed to 

 belong to the genus Cyrene ; but whether they are of fresh water, or of 

 marine origin, has not been satisfactorily determined. 



The beds of Coal appear to be of very limited extent, and not likely 

 to be sixfficiently productive for economical purposes ; their occurrence in 

 such a situation, is, however, highly interesting to the geologist, and 

 proves how much the existence of a deposit may depend upon local 

 causes. 



The organic remains are but few ; traces of lignite or charred wood 

 occur in the Iron sand ; impressions of ferns, in the coal shale ; and the 

 casts and remains of bivalves, in the limestone. 



2. Tilgate Limestone, &c. (p. 37). The strata designated by this 

 name, are fully described in the body of the work ; in this place it is only 

 necessary to recapitulate the more important points. These deposits 

 consist of thin beds of Mmestone and sandstone, which repose on Blue 

 clay, and correspond in so many particidars with the Purbeck, that there 

 is every reason to conclude they belong to that formation, and form a 

 protrusion through the Iron sand by which they are surrounded (vide 

 p. 58). They contain the remains of four or five species of vegetables, 

 bearing a distant resemblance to recent tropical plants ; nine or ten kinds 

 of univalves and bivalves ; several genera and species of fishes ; three 

 species of Turtle ; and one or more gigantic animals of the lizard tribe, 

 besides the bones, teeth, &c. of unknown animals, and perhaps of birds ? 



The remains of turtles, fishes, lizards, &c. occur in the Purbeck Hme- 

 stone, and the latter also corresponds in its chemical characters with that 

 of Tilgate ; it therefore appears unnecessary to renew the discussion on 

 their supposed identity ; and I shall only remark, that the fossils collected 

 since the former part of this volume was written, serve to confirm the 

 opinion therein advanced. 



3. The Weald clay (p. 61), is characterized by the Sussex marble, 

 which has commonly been supposed to be of fresh water origin, from the 

 presumption, that the univalves it contains, are related to the recent 

 HeUx vivipara. But if the observations of Mr. G. B. Sowerby (vide 



Q Q 2 



