THE MESEOSERE. 409 



ticaUy arid, but not cold. The association of cold and arid cUmates during 

 the Permian, however, suggests that cold or cooled chmates persisted during 

 much of the Triassic. The conformity between the Triassic and Permian red 

 beds throughout most of the Great Plains, and between gypsiferous beds in 

 theBlack HUls, indicates the continuityof aridcUmates atleast durmg these two 

 periods. Red beds, usuaUy with gypsum, and sometimes with salt, are found 

 along the eastern base of the Rockies, from British America to New Mexico, 

 indicating that the Great Plains and foot-hills had an and climate during the 

 Mesophytic, as well as to-day. Chamberlin and SaUsbury (1906 : 3 : 26) state 

 that " the Triassic beds of this region are not always readily distmgmshed from 

 the Permian on one hand and the Jurassic on the other. So difficult is the 

 separation that the Trias and Juras of this region are often grouped under the 

 name of Jura-Trias." In the interior basins red beds are also abundant, 

 usually associated with gypsum or salt. 



The difficulty of assigning the red beds of the Great Plains defimtely to the 

 Triassic or Jurassic indicates that the aridity of the Permian and Triassic con- 

 tinued into the Jurassic (Chamberlin and Salisbury, 1906: 3: 63, 94). Thus, 

 while the general climate of the Jurassic is regarded as genial, the geologic 

 evidences of aridity in the interior of North America are checked by the abun- 

 dance of small cycads in this region (Wieland, 1905 : 52, 55) and by the zooic 

 evidences of climatic zones (Chamberlin and SaUsbury, I. c, 79). The evi- 

 dence as to the climate of the Comanchean is more or less ambiguous, but in 

 general it indicates that the deformation at the close of the Jurassic had its 

 expected effect in producing a cooled cUmate. Em-opean fossils are thought 

 to indicate the existence of zones, as well as the presence in central Europe of 

 a climate like that of temperate America to-day. The fossil plants, especially 

 the cycadeans, from the Comanchean of the Rocky Mountain and Pacific 

 regions indicate a subtropical climate. 



THE MESEOSERE. 



Permian succession. — ^The Permian was characterized for some time by the 

 declining Paleophytic vegetation, as well as by the new flora of the Meso- 

 phytic. It seems probable that they marked two distinct developmental and 

 structural divisions of the total vegetation. The development in the relict 

 Paleophytic vegetation belongs to the next section, and will not be further 

 considered here. The persistence of Cordaites and the appearance of Saportea 

 and Baiera suggest the occurrence of a gymnospermous climax, distinct from 

 that associated with the Glossopteris flora. The latter, moreover, may have 

 shown two climax zones about the centers of glaciation. The general course 

 of the sere must have been the same in both climaxes. Charads probably 

 initiated the hydrosere, Uchens and mosses the xerosere. Equisetites and 

 reduced Calamites probably dominated the swamps, while ferns and pteri- 

 dosperms formed the stages corresponding to the herbaceous, grass, and scrub 

 associes of to-day. The genera of these stages were probably different for 

 each climax. Pecopteris, Sphenopteris, Goniopteris, CalKpteris, and Taeniop- 

 teris were typical of the lycopodean and supposed gymnospermous climaxes, 

 while Phyllotheca, Schizaneura, Neuropteris, Glossopteris, and Gangamopteris 

 were characteristic of the Glossopteris flora, which may well have been differ- 

 entiated into a graminoid climax of Glossopteris, a scrub climax of Voltzia 



