400 



THE WONDERS OF GEOLOGY. Lect. IV. 



The specimen from Sussex, fig A, is remarkable for the double 

 prominences on the scales. I extracted a small cone from 

 the lignite beds at Brook Cliff, which may possibly be the 

 fruit of the pine-trees of the fossil forest in that locality : a 

 cone resembling that of the Norfolk Island Pine has been 

 found in the dirt-bed of Portland. 



Four small carpolithes, and leaves of nine or ten (sup- 

 posed) species of cycadeous plants, are described and figured 

 by Dr. Dunker, from the Wealden of Germany.* 



24. Univalve shells of the Wealden. — The du- 

 rable remains of molluscous animals are most abundant ; 

 thick beds of limestone, spread over wide areas, and chiefly 

 composed of but three or four species of bivalves and uni- 

 valves, being a constant character of this group of deposits. 

 The prevalent shells belong to a few common fresh-water 

 forms, as Paludina, Cyclas, Unio ; three or four other 

 fluviatile, and an equal number of marine genera, the latter 

 being very sparingly distributed, make up the conchology 

 of the Wealden. Of the Cyclas, a fresh-water bivalve 

 which we have already noticed as abounding in certain 

 tertiary strata, upwards of forty species have been deter- 

 mined : of the Unio, a well-known fluviatile mussel, ten or 

 twelve species : and of the river snails, the Paludince, a 

 like number. It is worthy of remark, that of the common 

 lacustrine snails, the Limncea, so abundant in the fresh-water 

 tertiary beds of the Isle of Wight, but one wealden species 

 is known ; and of the PlanorbL% its constant associate in 

 those deposits, and in our ponds and lakes, one only has 

 been detected. f The conch ological fauna of the Wealden 

 is, in fact, rigidly fluviatile. In some parts of the lower 

 beds, layers of oysters occur, and occasionally a stray marine 



* Mon. Nord. Weald. Tab. TT. IV. VII. pp. 16, 21. 

 f Ibid. Tab. X. figs. 1, 2. Planorbis Inglesi, and Limncea Hennei, 

 of Dr. Dunker. 



