XIII THE GEOLOGICAL EVIDENCES OF EVOLUTION 399 



sphere and fixed in the solid state. These great beds of 

 graphite, therefore, imply the existence of abundance of 

 vegetable life at the very commencement of the era of which 

 we have any geological record.^ 



Ferns, as already stated, begin in the Middle Silm^ian forma- 

 tion -with, the Eopteris Morrieri. In the Devonian, we have 79 

 species, in the Carboniferous 627, and in the Permian 186 species ; 

 after which fossil ferns diminish greatly, though they are 

 found in every formation ; and the fact that fully 3000 living 

 species are known, while the richest portion of the Tertiary in 

 fossil plants — the Miocene — has only produced 87 species, Avill 

 serve to indicate the extreme imperfection of the geological 

 record. 



The EquisetaceiB (horsetails) which also first appear in 

 the Silurian and reach their maximum development in the 

 Coal formation, are, in all succeeding formations, far less 

 numerous than ferns, and only thirty living species are knoAvn. 

 Lycopodiacese, though still more abundant in the Coal form- 

 ation, are very rarely found in any succeeding deposit, though 

 the living species are tolerably numerous, about 500 having 

 been described. As we cannot suppose them to have really 

 diminished and then increased again in this extraordinary 

 manner, we have another indication of the exceptional nature 

 of plant preservation and the extreme and erratic character of 

 the imperfection of the record. 



Passing now to the next higher division of plants — the 

 gymnospermSj— we find Coniferse appearing in the Upper 

 Silurian, becoming tolerably abundant in the Devonian, and 

 reaching a maximum in the Carboniferous, from which form- 

 ation more than 300 species are kno^vn, equal to the 

 number recorded as now living. They occur in all succeeding 

 formations, being abundant in the Oolite, and excessively so 

 in the Miocene, from which 250 species have been described. 

 The allied family of gymnosperms, the Cycadace^, first appear 

 in the Carboniferous era, but very scantily ; are most abundant 

 in the Oolite, from which formation 116 species are kno^vn, 

 and then steadily diminish to the Tertiary, although there are 

 seventy-five living species. 



"We now come to the true flowering plants, and we first 

 ^ Sir J. William Dawson's Geological Ilistwy of Plants, p. 18. 



