548 THE UNIVERSE. 



to annihilate, sprang up on a heated and marshy soil, which 

 surrounded the lofty trees with thick, compact masses of 

 herbaceous aquatic plants, intended to play a great part in 

 the formation of coal. 



The luxuriant vegetation of the coal period was certainly 

 favored by the enormous heat which the terrestrial crust 

 still preserved, as also by the dampness of the atmosphere, 

 and very probably by the great abundance of carbonic acid 

 which it then contained. 1 



Although a thick and magnificent mantle of foliage cov- 

 ered the globe, everything wore a strange, gloomy aspect. 

 Everywhere rose gigantic horse-tails (Equiseta) and ferns, 

 drawing up an exuberance of life from the fertile and vir- 

 gin soil. The latter in their aspect resembled palms, and at 

 the least breath of wind waved their crowns of finely-cut 

 leaves like flexible plumes of feathers. A sky ever sombre 

 and veiled oppressed with heavy clouds the domes of these 

 forests ; a wan and dubious light scarcely made visible the 

 dark and naked trunks ; on all sides reigned a shadowy and 

 indescribable hue of horror. This rich covering of vegeta- 

 tion, which extended from pole to pole, was sad and silent, 

 as well as strangely monotonous. Not a single flower en- 



1 At the present time the atmosphere only contains a thousandth part of car- 

 bonic acid, whereas, according to Mons. A. Brongniart, there were at the carbon- 

 iferous period seven to eight parts in a hundred. This acid being an indispen- 

 sable part of the food of plants, to which it gives up all its carbon, its presence 

 easily explains the great development of the antediluvian forests of this period, 

 and as such a quantity of acid in the air would clearly have been fatal to animals 

 of a higher degree of development, such as mammals and birds, so none are met 

 with at that time. Reptiles and mammals only appeared when the plants and 

 trees, by their absorption of the carbonic acid as food, had necessarily purified the 

 atmosphere sufficiently to allow of animal life going on freely. 



