PHYSICAL GEOGRAPHY AND CLIMATE OF THE COAL PERIOD. 379 



In the Rocky Mountain region there were considerable bodies of 

 land, mainly in the Basin region, but their limits are not accurately 

 known. 



Again, it is almost certain that all the lands were comparatively 

 low. None of the great mountain-chains of the continent were yet 

 formed. It is also probable that the same was true of the other conti- 

 nents. Nearly all the high mountain-chains are either more recent in 

 their origin, or else in their principal groivth. In general terms, then, 

 the lands were smaller and lower, and the conditions more oceanic, 

 than at present. 



Climate. — The climate of the Coal period was undoubtedly charac- 

 terized by greater warmth, humidity, uniformity, and a more highly 

 carbonated condition of the atmosphere, than now obtain. Most of 

 these characteristics, if not all, are indicated by the nature of the vege- 

 tation : 



1. The ivarmth is shown by the existence of a tropical or ultra- 

 tropical vegetation. Of the present flora of Great Britain about one 

 thirty-fifth are Ferns, and none of these Tree-ferns. Of the Coal flora 

 of Great Britain about one half were Ferns, and many of these Tree- 

 ferns. At present in all Europe there are not more than sixty known 

 species of Ferns : in European Coal-measures there are nearly 350 * 

 species, and these are certainly but a fraction of the actual number 

 then existing. That this indicates a tropical climate is shown by the 

 fact that out of 1,500 species of living Ferns known twenty years ago, 

 1,200, or four fifths, were tropical species. The number of known liv- 

 ing Ferns is now about 3,000, f but the proportion of tropical species is 

 still probably the same. Even in the tropics, however, the proportion 

 of Ferns is far less than in Great Britain during the Coal period. 

 Again, Tree-ferns, arborescent Lycopods, Cycads, and Araucarian Coni- 

 fers, are now wholly confined to tropical or sub-tropical regions. The 

 prevalence of these tropical families and their immense size, compared 

 with their congeners of the present day, would seem to indicate not 

 only tropical but «^m-tropical conditions. And these conditions pre- 

 vailed not only in the United States and Europe, but northward into 

 polar regions ; for in Mellville Island, 75° north latihide, and Spitz- 

 bergen, 77° 33' north latitude, have been found coal-strata containing 

 Tree-ferns, gigantic Lycopods, Calamites, etc. 



2. The humidity is indicated by the fact that Tree-ferns and arbo- 

 rescent Lycopods are most abundant now on islands in the midst of the 

 ocean ; and further by the great extent of the Coal swamps, and per- 

 haps also by the general succulence of, or the predominance of cellular 

 tissue in, the plants of that period. 



* Lesquereux. \ Nature, August, 1876. 



