i8 PLANT GEOGRAPHY 



The second great vascular flora, though often termed 

 Mesozoic, in its origin overlaps, or is continuous with, 

 that first great " Reign of Acrogens " with which we 

 have been dealing. It differs in the proportion that 

 one group bears to another, besides being characterised 

 by advance and increasing variety in groups that had 

 appeared earlier, although by degeneration in others. 

 Its origin and centre of dispersion would seem to be 

 more definitely traceable than that of the Palaeozoic 

 flora, to be apparently southern. Here we first meet 

 with evidence of a division of the earth's surface into 

 distinct biological regions. 



While much of North America, Central Europe, and 

 Central Asia was apparently occupied, during the later 

 half of the Carboniferous age, by low-lying, moist, 

 forest-clad areas sinking intermittently below shallow 

 seas, there is stratigraphical as well as palaeobotanical 

 evidence that an enormous continental area was forming 

 to the south of the Tropic of Cancer, which seems to 

 have remained continuous into Rhaetic, if not into 

 somewhat later, times. The Lower Carboniferous or 

 " Culm " flora or, as perhaps it should be designated, 

 the Devoniano-Carboniferous flora with its abundance 

 of Lepidodendra, is found hi the south as hi the north. 

 Thus there is evidence that the vegetation of the world 

 was then singularly uniform. But from the latter part 

 of the Carboniferous era Africa south of the northern 

 tropic seems to have been united to Madagascar and 

 India in a vast and elevated continental area, seeing 

 that in large central and southern lake-areas no less 

 than 18,000 feet of " Karroo beds " were laid down. 

 The beginning of the period would seem to have been 

 marked by intense glaciation ; and such conditions have 

 been traced for the same period in Brazil, the Argentine, 

 the Falkland Islands, Tasmania, Victoria, New South 

 Wales, and Queensland. This is represented by the 

 great basal boulder-beds known in the various continents 

 as the Dwyka Conglomerate, the Talchir beds, and the 

 Bacchus Marsh beds. Above these come great thick- 

 nesses of strata destitute of marine shells, but containing 

 plant-remains and other indications of land and fresh- 

 water conditions. To these beds, the approximate age 

 of which is indicated by the term " Permo-Carbon- 

 iferous," the name Gondwana system is applied, from 



