476 THE PERMIAN PERIOD 



ment. The salient facts in connection with the physical conditions 

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

 certain questions relative to the life arise: (i) 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 conditions 

 by migrating from one area to another as the adverse conditions 

 shifted (hypothetically)? (4) Did its composite experience embrace 

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



In the early days of geology it was commonly held that a com- 

 plete 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 at 

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

 the following era. But 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 bring- 

 ing more and more evidence of this kind to light. 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 b/e great. 



Plants. The change in the vegetation was rather marked in 

 America, though not, at the outset, radical. Of the 107 species of 

 plants recorded from the lowest Permian beds of West Virginia and 

 Pennsylvania, 22 are found in the Coal Measures below. This and 

 other similar facts show that a rather profound change was in 

 progress, but that it was not abrupt. But a small part of the total 

 floral changes of the Permian appears in the American record, as 

 now known; but the nature of the early change is indicated distinctly. 

 Lepidodendrons disappeared, Sigillaria became rare, and Calamites 

 were greatly reduced. The general features of the fern group re- 

 mained much as in the preceding period, but most of the species and 

 many of the genera were new. Cordaites continued, and initial 

 forms of Ginkgos appeared, giving to the flora a Mesozoic cast. 



In Europe Carboniferous types declined as the period advanced, 

 and the general aspect of the flora was that of poverty. Of the new 



