386 THE WORLD OF LIFE CHAP. 



immediate cause is (as I have endeavoured to show here), 

 the slow but continuous changes of the earth's surface as 

 regards contour, altitude, climate, and distribution of land 

 and water, which successively 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 process has worked 

 throughout the geological ages, the world's surface ever 

 becoming more complex through the action of the lowering 

 and elevating causes on a crust which at each successive 

 epoch has itself become more complex. This has always 

 resulted in a more varied and generally higher type of 

 vegetation, 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 marvellous living, moving, self-supporting, and 

 self - reproducing structures, must be many million times 

 greater than those which conceived and executed the modern 

 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 complexity of structure 

 during the last century. But if we take account of the 



