668 GEOLOGY 



The marked likeness of the floras associated with the glacial 

 deposits throughout these four continents is believed to be evi- 

 dence that there was land connection between them at the time 

 of the glaciation. The age of these glacial beds is not absolutely 

 established; for the Carboniferous and Permian are not clearly 

 differentiated in the regions where the glacial formations occur. 

 Perhaps the best judgment that can be formed now is that the 

 Paleozoic glaciation culminated in the early part of the Permian 

 period. 



CLOSE OF THE PALEOZOIC ERA 



The close of the Paleozoic era was marked by much more con- 

 siderable geographic changes than the close of any period since 

 the Proterozoic, though they may be said to have been in progress 

 during the Permian period, rather than to have occurred at its close. 



The more important geographic changes in North America 

 which were far advanced by the close of the Paleozoic, were (1) the 

 development of the Appalachian mountain system at the western 

 border of Appalachia; (2) the deformation of the surface of Appa- 

 lachia; (3) the development of the Ouachita Mountains; (4) the 

 final conversion of the larger part of the area between the Great 

 Plains and Appalachia from an area of deposition to an area of 

 erosion; and (5) the restriction at the west of the area of sedimenta- 

 tion in the western interior. 



Such extensive geographic changes, involving the conversion of 

 extensive areas from sea bottom into land, must have caused pro- 

 found changes in the circulation of ocean waters, in the climate of 

 many localities, and in the distribution of terrestrial and marine life. 



THE LIFE OF THE PERMIAN 



The life of the Permian must be interpreted in connection with 

 the extraordinary physical conditions which formed its environ- 

 ment. Between them and the life there must have been reactions 

 and adaptations of the utmost significance, if we could surely read 

 them. At no period save our own were the phenomena so pro- 

 nounced, and hence, with little doubt, so rich in possible instruction 

 as to the adaptation of life to extreme conditions. 



