THE SEVEN AGES OF PLANT LIFE 41 



flourishing in the Carboniferous times have become 

 extinct. 



The Cycad-like plants, however, were far more numer- 

 ous and varied in character and widely spread than they 

 ever were in any succeeding time. Still, no flowers 

 (as we understand the word to-day) had appeared, or 

 at least we have no indication in any fossil hitherto 

 discovered, that true flowers were evolved until towards 

 the end of the period (see, however. Chapter X). 



The newer Mesozoic or Upper Cretaceous period 

 represents a relatively deep sea area over England, and 

 the rocks then formed are now known as the chalk, 

 which was all deposited under an ocean of some size 

 whose water must have been clear, and on the whole free 

 from ordinary debris, for the chalk is a remarkably homo- 

 geneous deposit. From the point of view of plant his- 

 tory, the Upper Mesozoic is notable, because in it the 

 flowering plants take a suddenly important position. Beds 

 of this age (though of very different physical nature) are 

 known all over the world, and in them impressions of 

 leaves and fruits, or their casts, are well represented. 

 The leaves are those of both Monocotyledons and 

 Dicotyledons, and the genera are usually directly com- 

 parable with those now living, and sometimes so similar 

 that they appear to belong to the same genus. The 

 cone- bearing groups of the Gymnosperms are still 

 present and are represented by a number of forms, but 

 they are far fewer in varieties than are the groups of 

 flowering plants — while the Cycad-like plants, so im- 

 portant in the Lower Mesozoic, have relatively few- 

 representatives. There is, it almost seems, a sudden 

 jump from the flowerless type of vegetation of the 

 Lower Mesozoic, to a flora in the Upper Mesozoic which 

 is strikingly like that of the present day. 



The Tertiary period is a short one (geologically 

 speaking, and compared with those going before it), and 

 during it the land level rose again gradually, suffering 

 many great series of earth movements which built most 



