THE FOSSIL RECORD 27 



we know practically nothing. At present it is 

 only the Flora of the Upper Devonian which is 

 at all well known. 



The vast masses of ancient rock known as 

 the Silurian and the Cambrian do not come 

 into consideration in this book, for we have 

 but little knowledge of land-plants from these 

 strata; supposed discoveries of Silurian Ferns 

 and Club-mosses are still open to doubt, 

 though it appears certain that vascular plants 

 must have existed at least as early. Some well- 

 preserved seaweeds occur in Silurian and even, 

 perhaps, in Cambian rocks, but the subject 

 of the history of the Algae, though very inter- 

 esting, does not fall within the limits we have 

 laid down. 



Broadly speaking, there are only four really 

 well-characterised Floras of the past, so far as 

 we know 



I. The Tertiary and Upper Cretaceous; the 

 modern Flora, or Era of the Angio- 

 sperms. 



II. The Mesozoic Flora, or Era of the 

 Gymnosperms. 



III. The later Palaeozoic Flora, or Era of the 

 primitive Seed-plants and Cryptogams. 



IV. The early Palaeozoic Flora, or Era of the 

 Algae. 



