392 



THE WONDERS OF GEOLOGY. Lect. IV. 



The shells in the clays have undergone but little change, 

 and in many examples, the epidermis and even ligament 

 are preserved ; in the limestones, the substance of the shells 

 is converted into spathose carbonate of lime ; in the sand- 

 stones, casts of the interior of the shells are often the only 

 vestiges. With these general remarks, I pass to the con- 

 sideration of the fauna and flora of the Wealden epoch. 



20. Fossil vegetables. — From the abundance of car- 

 bonized vegetable remains in many of the laminated shales 

 and clays, and the occurrence of lignite, or brown- 

 coal, in masses and layers, which sometimes alternate 

 with shales abounding iu fresh-water bivalves, a striking 

 analogy is presented to some of the divisions of the Coal 

 measures; but there are no beds of coal of any economical 

 value in the English Wealden.* In Hanover, however, this 

 formation contains an extensive coal field, which furnishes 

 excellent fuel. 



But notwithstanding the prevalence of vegetable matter 

 in the strata, specimens exhibiting the internal structure 

 of the plants, with any tolerable distinctness, are very 

 rare ; and though my researches were for many years 

 unremitting, I have obtained but few fossil plants that 

 admit of satisfactory conclusions as to the organization and 

 affinities of the originals. I shall restrict my observations 

 to a brief account of the principal kinds, and the circum- 

 stances under which they occur. 



Ferns. — Entire layers of the calciferous grit of Tilgate 

 Forest are so full of minute portions of carbonaceous 

 matter, f as to present a dark mottled colour ; and upon 

 examining the imbedded particles, they prove to be the 

 detritus of plants ground to pieces by agitation in water 

 loaded with sand and mud. Specimens in my possession 



* Sec Geology of the South-East of England, p. xviii. ; and Fossils of 

 the South Downs, p. 35, for an account of an unsuccessful trial for coal 

 at Bexhill. f Fossils of Tilgate Forest, Plate Z,fig. 6. 



