394 PALAEOZOIC TIME. 



considered that the land must have been but little elevated, and 

 quite uniformly so, — enough to drain the great salt marshes of their 

 salt, and not so high as to turn them into dry fields. It was not suf- 

 ficient that there should be land and Carboniferous vegetation ; for 

 without the wet, swampy lands — wet with fresh waters, and very 

 wide in extent — the great accumulations of vegetation and im- 

 mense coal fields would not have been made. 



There is a similarity between the continents, also, in the character 

 of the oscillations which occurred in the course of the Carboni- 

 ferous period, which submerged the land after material for a coal 

 bed had accumulated, and buried it for long keeping beneath sand- 

 stones and shales, and then brought it again to the surface for 

 renewed verdure and another coal bed ; and so on in many succes- 

 sions. 



The Millstone grit, which preceded the Coal measures in Europe 

 as well as America, is evidence of a degree of correspondence in 

 that upward movement of the continents through the waves which 

 ushered in the epoch of the Coal Measures ; and the prevalence 

 and wide distribution of the limestone of the Subcarboniferous 

 period, which next preceded, mark another cotemporaneous move- 

 ment, — a very general submergence preceding the emergence just 

 alluded to. Moreover, in both continents, some thin coal beds 

 were formed in the Subcarboniferous period. 



Contrast between America and Europe. — While the two continents 

 were at times concordant in their general movement, there was 

 apparently a contrast during the Coal period in the moisture of the 

 two, which may in part, at least, be attributed to climate. This is 

 apparent in the vastly larger coal fields of America. Guyot has 

 called America the forest-continent, a character it now bears because 

 of its moist climate, or more abundant rains ; and it is probable 

 that it presented this peculiarity with the first appearance of vege- 

 tation over its surface. 



IV. Life. 



1. System of progress. — The Animal kingdom began with Radiates, 

 Mollusks, and water Articulates ; included Fishes, the lower Ver- 

 tebrates, in the Devonian ; and Reptiles in the Carboniferous age. 

 With each period the progress was upward towards a fuller and 

 higher display of the system of life. 



It is important to observe, in this connection, that the length of the Age 

 of Mollusks, or Silurian age, as shown on p. 386, was three or four times that 

 of either the Devonian or the Carboniferous. This fact, in connection with 



