INIKODTTCTION. O 



the Imperfection of tlie Geological Eecord, the facts unmistakably 

 point to a widespread change in the constitution, of northern floras 

 at the' close of the Permian era — a change ■which appears to have 

 been effected with comparative suddenness. As the result of 

 certain circumstances, evolutionary forces acted with increased 

 rapidity at this stage in the history of the plant-world. There is 

 always a danger in speaking of the change from one flora to another 

 as having been abrupt or sudden, as the expression implies an 

 occurrence at variance with our ideas of the course of action of 

 evolutionary forces. It must be remembered that the documents 

 from which the history of plant-life is compiled are exceedingly 

 fragmentary, and we cannot form any conception as to the interval 

 which separated one flora from another. In stating that the 

 character of the vegetation appears to have undergone an almost 

 sudden change, we simply mean that within a short period, as 

 measured by geological records, sweeping changes were effected in 

 the composition of the vegetation. 



There can be no reasonable doubt that at certain stages in 

 the evolution of floras there was a widespread alteration in the 

 relative preponderance of classes. It would seem that the march 

 of plant-life has been characterised by long- continued periods, 

 during which no fundamental changes were effected as regards 

 the balance of power among the different classes of plants, 

 succeeded at rare intervals by stages which were distinguished by 

 striking and comparatively rapid reorganisation, and by an 

 alteration in the dominant type. The older Triassic floras introduce 

 us to a new type of vegetation, which, with gradual additions and 

 modifications, persisted up to the end of the "Wealden period. In 

 the southern hemisphere the Permo-Carboniferous floras differ 

 but slightly from those of the Triassic epoch ; in India, for 

 example, the plant-beds of the Damuda and Panchet series have 

 afforded evidence of comparative continuity between the later 

 Palseozoic and the earlier Mesozoic vegetation. As we pass up 

 to the succeeding Eajmahal series a vegetation is met with which, 

 in essential features agrees with that of Ehsetic and Liassio age in 

 the northern hemisphere. It would seem, then, that in the south 

 the Mesozoic type of vegetation appeared at a somewhat later 

 period than in the north. There must have been a considerable 

 interval between the deposition of the Upper Damuda beds of 



