FLORAS OF THE OLDER STRATA. 473 



some connection with Australia on the one hand, and with extra 

 tropical South America on the other. "Western Europe has its Erica, 

 GenistesB, Lobelia, and Gladiolus, genera characteristic of the Cape, 

 while other European groups appear to have diverged from South 

 African stocks, but hardly any species cross the Khine or the Rhone, 

 or extend beyond Britain into Scandinavia. 



Succession of Plant Life. Geological history presents, in so far 

 as it is at present known, three types of vegetation, which correspond 

 with epochs of time. First the Primary flora, mainly cryptogamic 

 and coniferous; secondly the Jurassic flora, including cryptogams, 

 coniferae, and cycads ; thirdly the Cretaceous and Tertiary floras in 

 which the living types of exogens and endogens preponderate. The 

 oldest known plants in Europe are described by Dr. Hicks from 

 the slates of Corwen, under the name Berwynia : it is supposed 

 to be Lycopodiaceous. Slightly older land -plants in the United 

 States have been named Glyptodendron. The Silurian rocks are 

 poor in plant remains, and the well-known Pachytheca from the 

 Ludlow bone bed is almost the only type they yield. But with the 

 Devonian age a remarkable group of coniferous trees with a central 

 pith is found, together with tree ferns, Lycopodiaceous plants of the 

 Lepidodendron type, Sigillaroid trees, and numerous Equisetacese ; 

 and this flora presents no essential modification during the Carboni- 

 ferous Period, so that, from the point of view of land vegetation, the 

 Devonian and Carboniferous rocks are united together by a character 

 which divides them from the Lower Primary series. 1 It is not till 

 we come to the Trias that a new life-province appears, as indicated 

 by the existing type of solid-hearted coniferae, some of which were 

 closely allied to Araucaria, mixed with a varied succession of Cyca- 

 daceous plants. Coniferse and cycads include 9 of the 1 2 genera, and 

 1 1 species of the flora of the Lower Lias ; but the Inferior Oolite, 

 especially in the estuarine shales and sandstones of the Yorkshire 

 coast, yields a richer flora, comprising 41 genera and 130 species, 

 among which are 53 species of ferns, 23 cycads, and 7 types of 

 conifers. A cycad is found in the Oxford clay, and Yatesia, 

 Bucklandia, and other cycads are associated with Araucarites. 

 A species of Pinites is found in the Kimmeridge clay. But the 

 Jurassic flora, though well preserved in some Indian and Australian 

 localities, is still too imperfectly known to permit of it having more 

 than a stratigraphical interest, for it is impossible to infer from it 

 either the descent of the plants or their geographical distribution. 



With the Cretaceous Period, however, and the discoveries made at 

 Aix-la-Chapelle by Dr. Debey, 2 we meet with a new phase of plant 

 life. Pandanus had already yielded a representative in the Lincoln- 

 shire limestone, and other Pandanaceous fruits had been found in the 

 Neocomian beds, \vhere Mr. Carruthers has also described the fruits 

 of conifers. The Gault, of Folkestone, has yielded cedars, and a species 

 of Sequoites and Pinites. The Cretaceous floras are remarkable for 



1 For enumeration of these floras see vol. ii. of this work. 



2 See Lyell, "Elements of Geology," Sixth Ed., 1865, p. 330. 



