456 SCIENCE PROGRESS. 



not familiar with the fossil botany of post-Carboniferous 

 rocks. Although on the whole the plants from Mesozoic 

 horizons occur in the form of casts and impressions, and 

 the number of well-preserved petrifactions is extremely 

 small in comparison with the material supplied by the older 

 rocks, yet there are many facts of considerable botanical 

 interest to be gleaned from an examination of Jurassic and 

 Cretaceous floras. There is perhaps a tendency on the 

 part of those whose main work is confined to recent plants, 

 but who occasionally refer to palseobotanical literature with 

 a view to giving a greater completeness to their conclu- 

 sions, to confine themselves to the botanical evidence 

 afforded by Palaeozoic plants. For this and other reasons 

 it is proposed to give a short resume of such data as we 

 possess as to the composition of some of the floras of more 

 recent geological age. 



The geological system to which the name Wealden was 

 first applied in 1828 has usually been placed by geologists 

 at the base of the Cretaceous formation. It would seem, 

 however, that some at least of the strata comprised under 

 the term Wealden are more closely linked by the animal 

 and plant fossils which they contain with the Jurassic rather 

 than with the overlying Cretaceous system. In England 

 the Wealden rocks are chiefly developed in the Weald 

 district of Kent and Sussex ; they occupy an oval-shaped 

 area, bounded by the chalk escarpment, which extends from 

 Folkestone Hill through the counties of Kent, Surrey, 

 Hants and Sussex, to the sea at Beachy Head. Strata 

 of the same age are also exposed on the south-west coast 

 of the Isle of Wight, between Compton Bay and Atherfield 

 Point, and to a less extent in the neighbourhood of Sandown, 

 on the opposite coast. Since the early part of the century 

 it has been recognised that the Wealden deposits are of a 

 freshwater and fiuviatile nature, and were evidently laid 

 down in the delta of a large river which flowed through a 

 low-lying country supporting a luxuriant vegetation. Frag- 

 mentary relics of the English Wealden flora were first 

 described about seventy years ago by Mantell, Fitton, 

 Brongniart and others, but it is only in recent years that 



