THE REVOLUTIONS OF THE CRUST OF THE EARTH. 351 



deposits were formed at the mouths of great rivers; for in several 

 places in the island of Disco trunks of trees more than 30 centimeters 

 (13 inches) in diameter have been found buried in the earth, and some- 

 times in a vertical position, which proves that these trees have vege- 

 tated in latitudes where now a stratum of permanent ice covers the 

 barren rocks, • 



To show that climates were really at one time milder than they are 

 now, we may give as an example Iceland, which possessed formerly a 

 rich flora and magnificent forests. Now the dwarf birch, the weeping- 

 willow, and a few more or less hardy shrubs are the only remains of the 

 ligneous vegetation. Greenland also, as we know, was once completely 

 free of ice and covered with the verdure from which it derives its name. 



At certain periods the Polar Sea must have been not only entirely 

 free of ice, but also quite warm, for we find in its deposits corals, Eucri- 

 nites, and other Mollusca, whose living representatives inhabit warm 

 seas. The Carboniferous limestone, the, coal-beds, and especially the 

 magnesian limestone of the high latitudes, are also witnesses of a warm 

 and uniform climate, which extended to arctic regions, now the most 

 desolate. As further proof, in Prince Island, at Wilkie Point, at 70'^20'' 

 of north latitude and 119° 40' of west longitude, Captain MacClintock 

 found oolitic rocks, containing an ammonite {Ammonites MacGlintocJci) 

 and other oolitic shells. At Katmay Bay, near Behring's Strait, we find 

 the following oolitic fossils : Ammonites WossnessensMi, Ammonites hipleXy 

 Belemnites, Paxillosus, Unio liassinus. Sir E. Belcher found in the island 

 itt' Exmouth, 77° 16' latitude north and 98° 20' longitude west, upon an 

 elevated bank 570 feet long. (173'°. 28^, above the level of the sea, bones 

 which Mr. Owen recognized as belonging to the Ichthyosaurus.* To pro- 

 duce such effects the mean temperature should, according to M. Heer, be 

 elevated 16° centigrade, for we find in the Miocene flora of Spitzbergen 

 the beech, the plane-tree, the hazel-tree, and other species identical with 

 the fossils of Greenland, and he thinks the poplar and pine once grew 

 even upon the north pole. The Sequoia Langsdorjii is the most com- 

 mon tree of Ataukerluk Bay visited by M. Heer. The Sequoia sempervi- 

 reus is the recent representative of these fossil trees. It does not, how- 

 ever, extend beyond the fifty-third degree of north latitude ; for a mean 

 summer temperature of from 15° to 16° centigrade is necessary for its 

 existence. Fruits ripen only at a mean temperature of 17° to 18®. The 

 cold of winter cannot descend below one degree. 



To what must these great changes of climate of the polar region be 

 attributed? The eccentricity explains a part of the phenomenon, for 

 we know that, according to the precession of the apsides, sometimes it 

 produces conditions favorable to the extension of organisms, sometimes 

 it cools the hemisphere to such a degree that a large part of these 

 organisms are destroyed. Notwithstanding this alternation of uniform 

 climates and extreme climates produced by the eccentricity, this cause 



*J. Croll, Phil. Magaz., June, 1867, pp. 426, 427. 



