THE PERMIAN PERIOD 669 



The salient facts in connection with the physical conditions 

 of the Permian were glaciation and aridity. In view of these facts, 

 certain questions relative to the life arise: (1) Did it possess such 

 powers of adaptation as to meet its extraordinary environment 

 by adjusting itself to it? (2) Was it destroyed co-extensively 

 with the changes in environment? (3) Did it elude adverse condi- 

 tions by migrating from one area to another as the adverse con- 

 ditions shifted (hypothetic ally)? (4) Did its composite experience 

 embrace all these alternatives, and if so, what measure of each? 



The impoverishment of life. In the early days of geology it 

 was commonly held that a complete destruction of all things living 

 on the face of the earth attended the close of the Paleozoic era, 

 and that a re-creation followed; for in the state of knowledge of 

 that time, no Paleozoic species was known to have lived on into 

 the following era. Had it been known that glaciation pressed upon 

 the borders of the tropics from either side, and that aridity prevailed 

 over large areas elsewhere, it would have added great strength 

 to the conviction of a universal catastrophe to life. It is now 

 known that some species bridged the interval, and it is believed 

 that others underwent modifications which enabled them to live. 

 The progress of investigation is bringing more and more evidence 

 of this kind to light, and reducing the disastrous implications of 

 the record. Not only this, but the compensating effects of the 

 strenuous conditions in calling into play the powers of adaptation 

 and resistance of the organisms are coming to be recognized. 

 Notwithstanding all this, it appears that the life of the period was 

 greatly impoverished. A census made not many years ago gave 

 the known animal species of the Carboniferous period as 10,000, 

 while those of the Permian period were only 300. A census to-day 

 would probably increase the Permian ratio, but the contrast would 

 still be great. 



I. The Plant Life 



The change of the vegetation from the Carboniferous to the 

 Permian was rather marked in America, though not, at the outset, 

 radical. Of the 107 species of plants recorded from the lowest beds 

 referred to the Permian in West Virginia and Pennsylvania, 

 22 are found in the Coal Measures below, and 28 in the Permian 



