284 PAST CLIMATES AND CLIMAXES. 



"The close of the Paleozoic era was marked by much more considerable 

 geographic changes than the close of any period since the Algonkian. These 

 changes may be said to have been in progress during the Permian period rather 

 than to have occurred at its close. The changes in the relation of land and 

 water, and the deformation of strata mentioned in connection with the close 

 of the Carboniferous period, probably continued during the Permian" (639). 



"The life of the Permian can carry its full meaning and receive its full inter- 

 pretation only when put into association with the extraordinary physical con- 

 ditions which formed its environment. These were the most remarkable in 

 the post-Cambrian history of the earth" (640). 



"There is no question but there was a great reduction in the amount of life. 

 A census made a few years ago gave the known animal species of the Carbonif- 

 erous period as 10,000, while those of the Permian were only 300, or 3 per cent. 

 A census to-day would probably improve the Permian ratio notably, but the 

 contrast would still be great" (641-642). 



"The change in the vegetation from the Carboniferous to the Permian in 

 America was rather marked, but not, at the outset, radical. There was a pro- 

 gressive evolution as the period advanced. Of the 22 species found in the 

 Coal Measures, 16 are common to the Permian of Europe, so that only 6 species 

 which may be regarded as distinctive of the Coal Measures rise into the base 

 of the Permian, and with one exception, all the Coal Measures species had 

 disappeared before the second fossiliferous horizon of the Permian series is 

 reached. This implies that a rather profound change was in progress, but 

 that it was not altogether abrupt. In the southern hemisphere, if the glacial 

 bowlder beds be taken as markmg the base of the Permian, a transition seems 

 to have been in progress somewhat earlier, and to have become profound as 

 the natural result of the glacial invasions, which were followed by a new flora" 

 (642). 



"Those remarkable physical conditions that had dominated the land and 

 impoverished its fauna and flora in the Permian period still held sway during the 

 early part of the Triassic. In their general biological aspects, as in their physi- 

 cal, the two periods were akin, if not really parts of one great land period. (!) 

 Toward the close of the Triassic there was a pronounced change, attended by a 

 physical and biological transition toward the Jurassic stage, in which lower 

 levels and greater sea encroachment prevailed, with corresponding life phases." 



Similarly, the Cretaceous period, which closed the Mesozoic era, is no longer 

 regarded as a unit consisting of a lower and an upper series. Chamberlin and 

 Salisbury (1906 : 3 : 107) separate the two series as distinct periods, termed 

 the Comanchean and the Cretaceous. Moreover, the reasons assigned for 

 this change in classification lend color to the unavoidable assumption that the 

 appearance of a dominant angiospermic vegetation in the Cretaceous marks 

 the beginning and not the close of an era: 



"The distinctness of the Lower and Upper Cretaceous is, however, so great 

 that it seems, on the whole, in keeping with the spirit of the classification here 

 adopted, to regard the two series as separate systems, and the corresponding 

 divisions of time as separate periods. From the physical standpoint, the dis- 

 tinction between the Lower and Upper Cretaceous is greater than that between 

 the different parts of any Paleozoic system, as commonly classified, if the 

 Mississippian and Pennsylvanian be regarded as separate systems, and greater 

 than that between the Cambrian and the Ordovician, or between the Devonian 

 and the Mississippian (107). On the whole, therefore, the deformative 

 movements at the close of the Early Cretaceous period were considerable. In 



