CLIMATES OF GEOLOGIC TIME. 277 



been mild to warm throughout the world since the beginning of Cambric time; that there 

 was a marked increase of warmth in the Upper Cambric; and that these conditions were 

 maintained throughout the Ordovicic and the earlier half of the Siluric, since shallow- 

 water corals, reef limestones, and very thick dolomites of Siluric time are as common in 

 Arctic America as in the lower latitudes of the United States or Europe. 



The Siluric closed with an epoch of sea withdrawal and North America was again arid, for 

 now red shales, gypsum, thick beds of salt, and great flats of sun-cracked water-Umestone 

 were the dominant deposits of the vanishing seas. The marine faunas were as a rule 

 scant and the individuals generally under the average size. In North America no marked 

 mountain-making was in progress, but all along western Europe, from Ireland and Scotland 

 across Norway into far Spitzbergen, the Caledonian Mountains were rising. In eastern 

 Maine throughout Middle and Upper Siluric time there were active volcanoes of the 

 explosive type, for here occur vast deposits of ash. 



Deionic. — In the succeeding Lower Devonic time the Caledonian intermontane valleys 

 of Scotland and north to at least southern Norway were fiUing with the Old Red sandstone 

 deposits of a more or less arid climate. On the other hand, the invading seas of northern 

 Europe were small indeed, and their deposits essentially sandstones or sandy shales, but 

 in southern Europe and North America, where the invasions were also small and restricted 

 to the margin of the continent, the deposits were either limestones or calcareous shales. 

 The life of these waters was quite different from that of the earlier and Middle Siluric, and 

 entire stocks had been blotted out in later Siluric time, as is seen best among the graptohtes, 

 crinids, brachiopods, and trilobites, while new ones appeared, as the goniatites, dipnoans 

 or lung-fishes, sharks, and the terrible armored marine lung-fishes, the arthrodires. 



From this evidence we may conclude that the early Paleozoic mild cUmates were 

 considerably reduced in temperature toward the close of the Siluric and that even local 

 glaciation may have been present. Refrigeration may have been greatest in the southern 

 hemisphere, where the marine formations of Devonic time are coarse in character and, in 

 Africa, of very limited extent. Corals were scarce or absent here, and in South Africa the 

 glacial deposits of the Table Mountain series may be of late Siluric age ; if so, they harmonize 

 with the Caledonian period of mountain-making in the northern hemisphere. Warmer 

 conditions again prevailed in the latter hemisphere early in JVIiddle Devonic times, for 

 coral reefs, limestones, and a highly varied marine life with pteropod accumulations were of 

 wide distribution. On Bear Island workable coal beds were laid down in late Devonic time. 



Throughout the Devonic, but more especially in the Lower and Middle Devonic, the 

 entire area of the New England States and the Maritime Provinces of Canada was in the 

 throes of mountain-making, combined with a great deal of volcanic activity. At the same 

 time, many volcanoes were active throughout western Europe. 



Carbonic. — The world-wide warm-water condition of the late Devonic seas of the nor- 

 thern hemisphere was continued into those of the Lower Carbonic. These latter seas were 

 also replete with a varied marine life, among which the corals, crinids, blastids, echinids, 

 bryozoans, brachiopods, and primitive sharks played the important roles. Limestones were 

 abundant and with the corals extended from the United States into Arctic Alaska. Reefs of 

 Syringopora are reported in northern Finland at 67° 55' N., 46° 30' E., on Kanin Pensinula 

 (Ramsay). Even several superposed coal beds, and up to 4 feet in thickness of pure coal, of 

 early Lower Carbonic age, occur at Cape Lisburne, overlain by Lower Carbonic limestones 

 with corals. It is generally held that the world climate at this time was uniformly mild and 

 the many hundred kinds of primitive sharks lead to the same conclusion. There were in the 

 American Devonic 39 species of these sharks, in the Lower Carbonic not less than 288, in the 

 Coal Measures 55, and in the earUest Permic only 10. They had no enemies other than 

 their own kind to fear, and as the same rise and decline occurred also in Europe, we must 

 ask ourselves what was the cause for this rapid dying-out of the ancient sharks during 



