INTRODUCTION. 



The oldest assemblage of plant-remains with which we are 

 acquainted, in number sufficiently numerous to rank as a flora, 

 is that of the Upper Devonian and Lower Carboniferous rocks. 1 

 On the present evidence, the floras of these two geological 

 periods constitute one great paia^obotanical epoch, characterised 

 by remarkable uniformity throughout the world. 2 But when 

 we pass to the vegetation of the succeeding Upper Carboniferous 

 and Permian deposits we no longer find that it exhibits such 

 a worldwide uniformity of distribution. The plant-remains of 

 these two periods, although everywhere constituting another great 

 epoch in the history of the vegetable kingdom, are grouped 

 naturally in two well-marked botanical provinces. Thus one 

 flora existed in Europe, Northern Asia, and North America, 

 more or less contemporaneously with a dissimilar type of vege- 

 tation, confined for the most part to India and the Southern 

 Hemisphere. 



The southern flora differed remarkably in certain features from 

 that of the Northern Hemisphere. It is now generally accepted 

 that these two types of Permo-Carboniferous vegetation flourished 

 on two great continental regions, for the most part, but not 

 entirely, isolated, and widely separated from one another. The 



: The earliest known fossil plants are of Silurian ag-e. 

 3 Seward (03-), p. S31. 



b 



