PLANT'S GROWTH AND DECAY 107 



lost in vaporizing the water and bringing about the decom- 

 position. 



In the same way that human beings and animals of the 

 present day are of a very different and higher type to 

 those which first appeared on the earth's surface, so our 

 plant life has undergone a great alteration in character, 

 and as we trace by the light of geology the birth and 

 growth of vegetation, we are led to the conclusion that as 

 the earth cooled down, soil was first formed upon its rock 

 surface by the disintegrating action of water containing 

 carbon dioxide and by those processes to which we usually 

 give the name of "weathering." Spores of the lower 

 forms of plants, like lichens and mosses, then appeared, 

 and in their growth fixed the carbon and hydrogen from 

 the carbon dioxide and water vapor to the atmosphere. By 

 their decomposition they supplied the soil, which up to that 

 time had been of a purely mineral character, with the 

 organic constituents necessary for the growth of vegetation 

 of a higher order. 



This next form of vegetation, urged on in its growth by 

 the heat permeating from the cooling mass of the earth, 

 and fed by the excess of carbon dioxide and moisture in 

 the air and the virgin soil in which it grew, attained a 

 rapidity and luxuriance of growth which probably has 

 never been equaled. In type it consists chiefly of crypto- 

 gamic plants, such as club mosses, sedges, and other forms 

 of marsh vegetation, which, however, instead of growing 

 to a height of a few inches, attained enormous dimensions. 

 Dying down year by year they formed a densely packed 

 mass of vegetable matter, which undergoing the process of 

 checked decomposition of the same character as can be 

 recognized in the peat deposits of the present day, gradually 

 built up those masses of semi-decomposed vegetable matter 

 which were afterward converted by time, heat, and pres- 

 sure into the coal seams. 



The formation of peat is apparently due partly to fer- 

 mentation when exposed in its wet state to air, and partly 



