CLIMATIC CHANGES IN SOUTH AMERICA 625 



australis, Lepidodendron pedroatium* and Lepidophloios laricinus again as- 

 suming tlie role of coal-makers. Mingled with tliem are species of Gangamop- 

 teris, Glossopteris, and Phyllotheca, of the Gangamopteris flora. It is plain, 

 therefore, that an amelioration of climate sufficient to permit the return of 

 some of the northern types had already taken place ; and it is equally evident 

 that the absence of these types during the deposition of the lower beds was 

 due to climatic inhospitality rather than to a marine or other barrier. 



The paleobotanical material from the region of the Iraty black shale and 

 the succeeding beds of the Passa Dois series is confined to fossil stems. This 

 is the zone of the Pmronius hrasiUensis described by Brongniart, and of the 

 Lycopodlopsis derhtji and the Dadoxylon pedroi respectively described by 

 Renault and Zeiller, as well as of the Stereosternum tumidum Cope and 

 Mesosaunis irasiUeiisis McGregor. The Pasa Dois series has also furnished 

 another large Lycopodialean tree, probably belonging to Sigillaria, and two 

 new g>-mnosperms referred to Dadoxylon. The presence of Psaronius would 

 seem to indicate the return of Pecopterids, presumably of the Cladophleboid 

 group, to the southern Brazilian basins. This indication of further moderation 

 of the climate is corroborated by the woody structure of the fossil trees, in 

 which there are extremely obscure, if any. traces of annual rings, the growth 

 of the trees being apparently uninterrupted by seasonal changes. It is there- 

 fore permissible to conclude that at this time a mild and equable climate 

 once more prevailed, so that the surviving elements of the Permian cosmopoli- 

 tan flora were able freely to migrate and mingle with the survivors of the 

 Gangamopteris flora. 



The date of South American glaciation. which on the paleobotanical evi- 

 dence appears to have been contemporaneous with the Dwyka in South Africa, 

 the Talchir of India, and possibly the later Newcastle ice in Australia, would 

 seem to be at or extremely near the close of the Carboniferous. That the 

 severe cold was of short duration is shown by the early return of some of 

 the exiled northern Permo-Carboniferous plants. The fact that the post- 

 glacial moderation of tlie climate occurred some time before the extinction 

 of Lepidophloios and Lepidodendron conclusively sliows that the climatic 

 refrigeration could not have occurred later than the very early Permian. It 

 is interesting to note that the types first to return, and therefore presumably 

 the hardiest, belong to the Lycopods. 



The distribution in India, Australia, South Africa, and South America of a 

 terrestrial flora of varied elements like the older Gondwana flora necessitates 

 a distribution of the land masses in siich a way as to permit land plant 

 migration with absolute freedom between these regions. The testimony 

 of vertebrates and plants is mutually corroborative on this point. The author 

 inclines to recognize the important agency of an Antarctic land mass or con- 

 tinent, of which southern South America or South Africa may have been mere 

 lobes, in facilitating this free intermigration. 



The abstraction of carbon dioxide from air and sea and the storage of the 

 same in the coals, carbonaceous shales, and limestones of the Upper Car- 

 boniferous has never been equaled in any other period of geological history. 



• The employment of capital initials for names of species directly derived from names 

 of persons is not permitted by the rules for printing early adopted by this Society. 



