476 PAL^OBOTANY. 



pletely disappeared. The Calamites of the Coal-measures are 

 represented by true Horse-tails (Equisetites). Ferns and Coni- 

 fers are still abundant, and some of the latter ( Voltzia) are by 

 no means unlike existing forms. Lastly, there is an abundance 

 of remains of Cycadaceous plants (Pterophyllum, Podozamites, 

 &c.) 



The Jurassic and Lower Cretaceous deposits are similarly 

 characterised by an abundance of Cycads, Ferns, and Conifers, 

 the first of these in particular constituting a marked feature in 

 the vegetation. 



In the Upper Cretaceous period we have the first appearance, 

 in any quantity, of ordinary Angiospermous Exogens, similar to 

 those which predominate at the present day in the flora of 

 temperate regions. Besides Ferns and Cycads more or less 

 allied to Jurassic forms, we have now numerous Dicotyledonous 

 trees, such as the Oak, Beech, Fig, Poplar, Walnut, Willow, 

 Alder, &c., belonging to familiar genera now in existence. 

 Here, also, we have the first appearance, so far as is certainly 

 known, of the group of the Palms. 



Of the vegetation of the Tertiary period, it is sufficient to 

 remark here that now there is a marked predominance of 

 Angiospermous Exogens and of Endogens as compared with 

 Cryptogams and Gymnospermous Exogens. Not only is this 

 the case, but many of the Tertiary plants approximate closely 

 to existing forms, this approximation becoming more and more 

 marked as we recede from the Eocene and approach the Re- 

 cent period. 



Before closing this brief review of the succession of plants 

 upon the globe, it may be well to notice shortly a generalisa- 

 tion which was long since made by M. Adolphe Brongniart. 

 This distinguished observer, in dividing the series of stratified 

 deposits in accordance with the fossil plants contained in them, 

 named the Palaeozoic period the " Age of Acrogens," the 

 Secondary period (exclusive of the Cretaceous) the " Age of 

 Gymnosperms," and the Cretaceous and Tertiary periods the 

 " Age of Angiosperms." This generalisation, though still ex- 

 pressing a general truth, can only be accepted with consider- 

 able reservation. Gymnosperms, and even Angiosperms, are 

 not unknown in the Palaeozoic period ; and if the Sigillarioids 

 should be referred to the former group of plants, then the later 

 Palaeozoic period would have as good claim to be called the 

 " Age of Gymnosperms " as the Secondary period. Again, as 

 pointed out by Sir Charles Lyell, the Lower and Upper Creta- 

 ceous floras differ from one another in the most striking manner, 

 the Lower Cretaceous agreeing in this respect with the Jurassic 



