516 REVIEWS 



deposition. In spite of widespread glaciation at certain periods, the 

 Proterozoic era had, in the main, a rather warm, equable climate. This 

 is shown by the enormously thick limestone deposits (50,000 feet in 

 Canada), abundance of large Archaeocyathinae, widely distributed 

 graphites, and presence of coal. The Cambrian, with an abundance of 

 shallow-water life, had a uniformly warm temperature which continued 

 into the Ordovician and Silurian. The red shales, gypsum deposits, 

 salt beds, and scant, depauperate fauna of the late Silurian indicate 

 aridity and possible coolness, the latter expressed perhaps by local glacia- 

 tion (South Africa). The deposits of Northern Europe in the Devonian 

 probably marked a cool, somewhat arid climate, and the great change in 

 the life-forms in the Middle Devonian may be further evidence of the 

 same thing. The climate of the middle and later part of the Devonian 

 was warm; that of the Carboniferous, warm-temperate to subtropic. 

 The great variety of marine life, abundance of reef corals in high lati- 

 tudes, extensive coal deposits, subtropical flora, and large-sized insects, 

 all suggest this. The adverse climate of the Permian is clearly shown in 

 the glacial tillites, red shales, salt and gypsum deposits (to thickness of 

 3,300 feet), and depauperate, scanty fauna. The sweeping change in 

 the types of life seen in the Triassic is most convincing proof of climatic 

 severities at this time. Large trees (to 8 feet diameter), and their absence 

 of rings, luxuriant ferns, and thick deposits of limestones in high lati- 

 tudes, all suggest warmth. The late Triassic-Lias probably saw a 

 reduction of temperature, for of the Triassic ammonites (1,000 species) 

 none passed into the Jurassic, the insects were uniformly dwarfed, and 

 the corals, both numerically and geographically, were very much re- 

 stricted. The Jurassic was a period of remarkably warm, equable climate. 

 The wide distribution and variety of ammonites (15,000 species), their 

 presence with corals and marine saurians in very high latitudes, and the 

 very cosmopolitan, luxuriant floras are to be noted. The Comanchean- 

 Cretaceous marks the introduction of hardwood forests and may indi- 

 cate a cooler climate than the Jurassic; but the presence of magnolias 

 in Greenland and Alaska shows at least warm-temperate conditions 

 there. The Cretaceous is distinguished by a remarkable deployment of 

 the immense land reptiles and very thick limestone deposits. Climatic 

 conditions in the Tertiary are not sharply different from those of the 

 Cretaceous. Middle and late Eocene floras show many tropical marks, 

 Oligocene faunas are varied and large sized, especially the foraminifers 

 (nummulites), the Miocene shows a distribution of warm-temperature 

 plants in Spitzbergen and Grinnell Land, but the late Miocene was, at 



