NATURAL HISTORY OF CREATION. 117 



that the progi'ess of organic life has observed some cor- 

 respondence with the progress of physical conditions on 

 the sui'face. We do not know for certain that the sea, at 

 the time when it supported radiated, molluscous, and arti- 

 culated families, was incapable of supporting fishes ; but 

 causes for such a limitation are far from inconceivable. 

 The huge saurians appear to have been precisely adapted 

 to the low muddy coasts and sea margins of the time 

 when they flourished. Marsupials appear at the time 

 when the surface was generally in that flat, imperfectly 

 variegated state in which we fiud Australia, the i-egion 

 where they now live in the greatest abundance, and one 

 which has no highei' native mammalian type. Finally, it 

 was not till the land and sea had come into their present 

 relations, and the former, in its principal continents, had 

 acquired the irregularity of surface necessary for man, 

 that man appeared. We have likewise seen reason for 

 supposing that land animals could not have lived before 

 the carbonigenous era, owing to the great charge of car- 

 bonic acid gas presumed to have been contained in the 

 atmosphere down to that time. The surplus of this 

 having gone, as M. Brogniart suggests, to form the vege- 

 tation whose ruins became coal, and the air being thus 

 brought to its present state, land animals immediately 

 appeared. So also, sea-plants were at first the only 

 specimens of vegetation, because there appears to have 

 been no place where other plants could be produced 

 or supported. Land vegetation followed, at first simple, 

 afterwards complex, probably in conformity with an 

 advance of the conditions required by the higher class 

 of plants. In short, we see everywhere throughout the 

 geological histor}-, strong traces of a parallel advance of 

 the physical conditions and the organic forms. 



In examining the fossils of the lower marine creation* 



