THE BEGINNINGS OF LIFE. 141 



it every day more pure; but it was not till the ap- 

 pearance of a vegetation altogether new, abounding 

 in mighty trees, the source and origin of numerous 

 deposits of lignite, a vegetation which seems to have 

 covered the surface of the earth with vast forests, that 

 a great number of mammiferous animals, analogous in 

 all the essential features of their organization to those 

 that still exist in the world, appeared for the first time 

 upon its surface. 



c Would it not be fair to suppose from this, that our 

 atmosphere had now arrived at that degree of purity 

 which could alone comport with the active respiration 

 of warm-blooded animals, and prove alike favourable 

 to the development of plants and animals, whilst the 

 simultaneous existence of these two orders of beings, 

 and the inverse influence of their respiratory actions, 

 conduce to maintain our atmosphere in the state of 

 stability which is one of the remarkable characters of 

 the present period ?' 



Such, then, is the mighty round of things, such are 

 the interchanges ever taking place on the surface of our 

 globe. The inorganic is continually being fashioned into 

 the organic, and this after passing through successive 

 changes, and after having displayed the manifestations 

 of Life, is ever passing again into the inorganic, ever 

 again giving up its fashioning forces. c The crude and 

 formless mass of the air gradually organized in veget- 

 ables, passes without change into animals, and be- 

 comes the instrument of sensation and thought ; then 



