ABUNDANT VEGETATION. 67 



great density, that there is nothing existing at the present 

 time worthy to be compared with them, even in the hottest 

 climates. Such fertility appears to have been dependent 

 upon the conditions of the air and earth, the former con- 

 taining more carbonic acid (the food of vegetables) and the 

 latter a greater amount of warmth, than at present ; these two 

 circumstances, so favourable to the growth of plants, were 

 equally unfavourable to the existence of air-breathing 

 animals, to whom the carbonic acid would be fatal poison. 



Thus, in the mighty hands of Grod, the air was undergoing 

 a gradual purification, to fit it for the animals He intended 

 to create ; the polypi were extracting from the water all 

 the carbonate of lime it was absorbing from the air and 

 earth, and fixing it in the soil, to be of use in a hundred 

 ways at some future time, while the vegetation growing in 

 abundance extracted it from the air, and fixed its carbon in 

 their leaves and substance generally ; these vegetables, 

 decaying and falling upon the surface of the earth, accu- 

 mulated there for ages, and formed a carbonaceous matter 

 which was afterwards changed by time and pressure into 

 coal. The same thing (on a very much smaller scale) is 

 taking place in the tropical forests of the present age ; 

 there the surface-soil is quite black, and consists of nothing 

 but decayed leaves and wood for several feet in depth, but 

 in the present time . there are hosts of insects, every one of 

 which feeds upon this vegetable matter, preventing to a great 

 extent its accumulation, while in the former age there was 

 nothing to destroy it when once deposited on the ground ; 

 so that the carbon of these forests of the secondary period, 

 existing through perhaps tens of thousands of years, 

 extracted from the air a sufficient quantity of vegetable car- 

 bonaceous matter to produce thick seams of coal, even when 

 compressed by the superincumbent strata. These forests were 

 subject from time to time to inroads of the sea produced by 

 the before-mentioned causes, and thus it is found that the 

 seams of coal are often buried by several hundred feet of sand, 

 clay, shale, &c., above which the same growth recommenced 

 to form a second strata of coal, and ages must have elapsed 

 whilst each of the numerous seams which interstratify the 



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