324 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



between the mineral and animal kingdoms, tlie latter not assimilating 

 directly inorganic substances. Plants decompose the carbonic acid of 

 the air, under the influence of solar light, and set free the pure oxygen, 

 which is necessary for the respiration of animals ; also, they absorb the 

 inorganic salts and form albuminous azotic substances, which are en- 

 gaged in the production of the horny cartilaginous or bony frames and 

 the formation of the tissues of the animals. The humus is the iiro- 

 duction of the slow alteration of plants mingled with mineral substances. 

 It is found in a fossil state in all the deposits, and serves to promote 

 the development of plants to a more perfect organization. Upon an arid 

 rock first appear the lichens, which by their decay form enough earth 

 to allow the mosses to succeed them ; the grasses, finding the neces- 

 sary conditions for their development, follow the mosses, after which 

 any of the plants may dispute the new ground acquired for their nutri- 

 tion. The same succession takes place on a large scale in the organiza- 

 tion of the terrestrial crust. 



The preservation of the fossil remains of primitive plants is due to cer- 

 tain agents which prevent their decomposition. Water, for example, 

 destroys certain parts of a plant, while others are preserved in it for 

 quite a long time. The preservation of the soft and tender portions in- 

 dicate that these plants were soon covered with lime, and that they 

 were not deposited far from the place of their growth.* 



Some streams preserve their plants by depositing rapidly upon their 

 entire surface a stratum of calcareous matter which, gradually increas- 

 ing in thickness, shields them from all exterior action. To this process 

 we are indebted for the elements of a quite new science, paleophy tology, 

 which in many cases has opened the road to the discovery of the general 

 laws which have controlled the modification of climates. 



Plants are not only lound scattered here and there through the sedi- 

 mentary strata; their remains frequently form large deposits, such as the 

 beds of coal, lignite, and peat. In former times the products of the de- 

 composition of these deposits, such as bitumen and petroleum, were found 

 in such abundance, that their exploitation equaled in importance that 

 of coal, which, with iron, forms the basis of great industrial wealth. 



Coal is quite abundant in Europe; England, Belgium, France, 

 Prussia, Silesia, Bohemia, Hungary, possess mines of more or less im- 

 portance. Scandinavia, Russia, Greece, Italy, have, we may say, no coal- 

 deposits. Of other parts of the world, America is the most richly gifted, 

 while Australia possesses the least. 



The value of all the coal-deposits has been calculated by the Prussian 

 engineer, Mr. Carmel. He compares the whole amount to a solid mass 

 of 44,800,000,000 cubic meters (58,000,000,000 cubic yards). He at the 

 same time allays the apprehensions often expressed that this precious 

 combustible will be exhausted by its enormous consumption, which an- 

 nually draws from the earth a hundred and twenty-five million tons. This 



* F. Uuger, ChJoris protogwa, 1847, p. iv. 



