GEOGRAPHICAL VICISSITUDES OF PLANTS. 297 



It is doubtful whether our British flora contains 

 a soHtary member which was then hving, unless 

 they are represented by Club-mosses, Horsetails, 

 and Ferns. Our common Bracken [Pteris aqinlind) 

 may have been a spectator ; and the Cycadaceae of 

 the Cape, the Brazils, and Australia, are undoubtedly 

 lineal descendants of the forms which grew so abund- 

 antly in these latitudes during the early Oolitic 

 Period. 



Whatever may have been the composition of the 

 terrestrial flora in what is now England, during the 

 age just mentioned, it must all have been swept 

 away by the great change which took place during 

 the latter part of the Cretaceous Period, for all the 

 dry land was submerged, and a tolerably deep sea 

 eventually covered it, along whose bottom the " white 

 chalk " of England was slowly elaborated. The 

 chalk has been eaten away on every side since it 

 was upheaved and converted into dry land, but it 

 still extends from Ireland to Bordeaux, and from 

 Sweden to the Crimea — an area which will give some 

 idea of the extensive Cretaceous ocean, and which will 

 convey to the mind what a large tract of dry land, 

 with its crowds of plants, must have been sub- 

 merged before that Cretaceous ocean could have 

 been formed. 



Flowering plants of familiar types, allied to our 

 Oaks, Maples, etc., had appeared upon the earth 

 before the Cretaceous ocean was in actual existence ; 



