416 THE WORLD OF LIFE 



open new and unoccupied places in nature, to fill which some 

 previously existing forms become adapted through variation 

 and natural selection. I have sufficiently shown how this proc- 

 ess has worked throughout the geological ages, the world's sur- 

 face ever becoming more complex through the action of the 

 lowering and elevating causes on a crust which at each succes- 

 sive epoch has itself become more complex. This has always 

 resulted in a more varied and generally higher type of vegeta- 

 tion, and through this a more varied and higher type of animal 

 life. 



The remote but more fundamental cause, which has been 

 comparatively little attended to, is the existence of a special 

 group of elements possessing such exceptional and altogether 

 extraordinary properties as to render possible the existence of 

 vegetable and animal life-forms. These elements correspond 

 roughly to the fuel, the iron, and the water which render a 

 steam-engine possible; but the powers, the complexities, and 

 the results are millions of times greater in the former, and we 

 may presume that the Mind which first caused these elements 

 to exist, and then built them up into such man^ellous living, 

 moving, self-supporting, and self-reproducing structures, must 

 be many millions times greater than those which conceived and 

 executed the modem steam-engine. 



Variety of Inorganic Substances 



The recognised elements are now about eighty in number, 

 and half of these have been discovered during the past century ; 

 while twenty of them, or one-fourth of the whole, have been 

 added during the last fifty years. These last are all very rare, 

 but among those discovered in the preceding fifty years are 

 such now familiar and important elements as aluminium, 

 bromine, silicon, iodine, fluorine, and chlorine. So far as the 

 elements are concerned, our earth has doubled in apparent com- 

 plexity of structure during the last century. But if we take 

 account of the advance of chemical science, the knowledge that 

 has been obtained of the inner nature of the best-known older 



