146 OUTLINES OF FORESTRY. 



the present ; consequently, as urged by E. B. Hunt, it would 

 have occasioned increased heat at the earth's surface, and this 

 would have been one cause of a higher temperature over the 

 globe than the present. 



" During the progress of the Carboniferous period there was, 

 then, (1) a using up and storing away of the carbon of the 

 superfluous carbonic acid, and, thereby, (2) a more or less per- 

 fect purification of the atmosphere, and a diminution of its 

 density. In early time there was no aerial life on the earth ; 

 and, so late as the Carboniferous period, there were only rep- 

 tiles, myriapods, spiders, insects, and pulmonate mollusks. 

 The cold-blooded reptiles of low order of vital activity, cor- 

 respond with these conditions of the atmosphere. The after- 

 ages show an increasing elevation of grade and variety of 

 type in the living species of the land." 



