38 THE EVOLUTION OF PLANTS 



The subject of the geological history of the 

 Angiosperms themselves is a difficult one, because 

 the evidence, though abundant, is generally 

 dubious, most of the fossils being impressions of 

 leaves, from which it is often impossible to deter- 

 mine with any certainty the family to which 

 the plant belonged. The whole question needs 

 investigating afresh, but in the meantime a 

 few general conclusions may be given. 



Throughout the whole of the Tertiary period 

 Angiosperms were abundant; in fact, they were 

 dominant all through those long ages, much as 

 they are now. They were a varied class of 

 plants throughout, and a great number of our 

 living families have been recognised with more 

 or less certainty; Monocotyledons and Dicoty- 

 ledons are alike represented, the latter, as at 

 present, being much the more numerous. 



To a certain extent the same was the case 

 in the latter part of the Secondary period. The 

 Upper Cretaceous rocks, of an age more or less 

 corresponding to that of the Chalk, have yielded 

 a good many remains of Angiosperms, which at 

 that time were already the leading class of plants, 

 forming, in most places, the great bulk of the 

 Flora. The Cretaceous Angiosperms were on the 

 whole quite ordinary members of their class, so 

 far as the evidence enables us to judge. Birches, 

 Beeches, Oaks, Walnuts, Planes, Maples, Hoi- 



