CLIMATES OF GEOLOGIC TIME. 279 



Permic— Very early in Permic time the mild climate of the past was greatly changed; 

 the evidence is now overwhelming that throughout the southern hemisphere there was a 

 glacial period seemingly of even greater extent than that of the northern hemisphere during 

 the Pleistocene. This evidence is most easily seen in the wide distribution of the tillites 

 and the scratched and polished grounds over which the land ice moved in Africa, Australia, 

 Tasmania, India, and South America. In the northern hemisphere the evidence of ice 

 work is far less marked; but tillites occur near Boston, Massachusetts, and in the Urals, 

 and there is much evidence of thin and arid cUmates, seen in the widely distributed red 

 formations. Then, too, the land life of this time clearly indicates that a great climatic 

 change had taken place in the environment of the organic world. 



The grand cosmopolitan swamp floras of the Upper Carbonic, consisting in the main of 

 spore-bearing plants, such as the horse-tails (Equisetales) , the running pines, and club- 

 mosses (Lycopodiales), and the ferns, among which were also many broad-leaved evergreens 

 (Cordaites) and seed-bearing ferns (Cycadofilices) , were very largely exterminated in the 

 southern hemisphere at the beginning of Permic time. In the northern hemisphere, 

 however, the older flora maintained itself for a while longer, as best seen in North America, 

 but finally the full effects of the cooled and glacial climates were felt everywhere. Then 

 in later Permic time the old floras completely vanished, except the hardier pecopterids, 

 cycads, and conifers of the northern hemisphere, and with these latter mingled the migrants 

 from the hardy CTangamopteris flora originating in the glacial cUmate of the southern 

 hemisphere (White, 1907). Some of the trees show distinct annual growth rings, and hence 

 the presence of winters. It was these woody floras that gave rise to the cosmopolitan floras 

 of early Mesozoic time. 



With the vanishing of the cosmopolitan coal floras also went nearly all of the Paleozoic 

 insect world of large size and direct development, for the insects of late Permic time were 

 small and prophetic of modern forms. Then, too, they all passed through a metamorphic 

 stage indicating, according to Handlirsch, that the insects of earlier Permic time had 

 learned how to hibernate through the winters in the newly originated larval conditions. 



Our knowledge of the land vertebrates of late Paleozoic time is increasing rapidly and 

 it is becoming plainer that great changes were also in progress here. The vertebrates of 

 the Coal Measures, either the armored amphibians (Stegocephalia) or the primitive reptiles, 

 were still largely addicted to the "water habit" and lived in fresh waters or swamps, but 

 this was much changed by the arid climates and vanishing swamps of later Permic times, 

 and in the Triassic we meet with the first truly terrestrial reptilian faunas. 



A climatic change naturally must affect the land Ufe more quickly and profoundly than 

 that of the marine waters, for the oceanic areas have stored in themselves a vast amount 

 of warmth that is carried everywhere by the currents. The temperature of the ocean is 

 more or less altered by the changes of chmate, be they of latitude or of glaciation. The sur- 

 face temperatures in the temperate and tropical regions, however, are the last to be affected, 

 and only change when all of the oceanic deeps have been filled with the sinking cold waters 

 brought there by the currents flowing from the glaciated area. We therefore find that the 

 marine life of earlier Permic time was very much like that of the Coal Measures, and that 

 it was not profoundly altered even in the temperate zones of Middle Permic time (Zechstein 

 and Salt Range faunas) . Our knowledge of Upper Permic marine life is as yet very Umited 

 and will probably always remain so because of the world-wide subtraction of the seas from 

 the lands at that time. It was a period of continued arid chmates, and the marginal 

 shallow sea pans were, as a rule, depositing red formations with gypsum, and locally, as in 

 northern Germany, alternations of salt with anhydrite or polyhalite in tliicknesses up to 3,395 

 feet. In certain of these zones there were developed annual rings so regular in sequence 

 as to lead to the inference that they were the depositions of warm summers and cold winters, 

 enduring for at least 5,653 years (Gorgey, 1911). 



