702 GEOGRAPHICAL AND GEOLOGICAL BOTANY. 



predominance of Cycadeae (Zamites), which here appear in several new 

 genera, and the existence of Ferns with more highly organized foliage 

 than that of the genera of older formations. Algae, Fungi, Lichens, Ly- 

 copods, and Conifers also existed at this period, but no Angiospermous 

 Dicotyledons have yet been discovered. 



Oolitic System. The nature of the strata referable here is very diverse ; 

 the general character of the fossil vegetation consists in abundance of 

 Ferns proper, Equiseta, arid of Cycadeas, especially of those genera 

 (Zamites and Otozamites) approaching nearest to existing forms, and the 

 greater frequency of the Coniferse, Brachyphyllum and Thuytes, than in 

 the Lias. Cones of Araucarias have been found, as well as endogenous 

 plants allied to Pandanus and Arum. Algae, Marsileas, Lycopods are also 

 found. There are a large number of known species. The dirt-beds of 

 Portland are layers of soil with remains of Cycadaceous trees in an erect 

 position. Some of these are distorted by pressure into the shape of birds' 

 nests. 



Wealden System. This formation, remarkable as a freshwater product, 

 has afforded comparatively few species of plants, mostly congeneric, al- 

 though specifically distinct from those of the Lias ; but the proportion of 

 the Cycadaceae to the Ferns is smaller. Equisetum and Char a (the latter 

 by its* fruits) are represented. Dicotyledons have not been discovered. 



Cretaceous System. In this formation we are at once struck with the 

 diminution of Ferns, Equisetaceae, and allied forms, the reduction of the 

 species of Gymnosperms, and the appearance of Angiospermous Phanero- 

 gamia, chiefly dicotyledonous (Betula, Myrica, Salix, &c.), though traces 

 of Palms and Grasses have been met with. The Cycadaceae are still 

 numerous ; but they and the Coniferae do not more than equal the Dico- 

 tyledons. The genus Crednaria, supposed to belong to the last class, is 

 very characteristic of the Chalk formation. The Ferns and Equisetaceae 

 almost disappear. 



The fossil plants of the Upper Cretaceous system, the equivalent of 

 the Upper Chalk of this country, show a terrestrial flora in which all 

 the great subdivisions of the vegetable kingdom are represented. Dr. 

 Debey estimates the number of species at Aix at about 200, of which 

 67 are Cryptogams. Gleichenia, Lye/odium, and Asplenium among Ferns 

 have been identified as generically identical with the plants now so named. 

 Among Conifers, Cycadopieris closely resembles Sequoia ; Araucarias also 

 are found, but few Cycads. Pandanads existed, and, among Dicotyledons, 

 Figs, Oaks, Walnuts, Myrtles, and numerous Proteads, the structure of 

 the leaves of the latter being so perfectly preserved that even the stomata 

 may be seen. Attempts have been made even to correlate the genera with 

 existing types of Proteads ; but this is a very hazardous procedure, seeing 

 how variable the leaves of Proteaceae are. Still the general indications 

 point to a vegetation like that of Australia. 



3. Floras of the Tertiary System. 



The floras of this system form a more or less connected whole, 

 which is continued in the later strata into existing vegetation. 

 They are especially distinguished from those of older epochs by 



