256 THE RIDDLE OF THE UNIVERSE. 



and the great progress which dynamical and historical 

 geology have made during the century. 



The first division of the history of the earth must 

 be a separation of inorganic and organic geogeny ; 

 the latter begins with the first appearance of living 

 things on our planet. The earlier section, the 

 inorganic history of the earth, ran much the same 

 course as that of the other planets of our system. 

 They were all cast off as rings of nebula at the 

 equator of the rotating solar mass, and gradually 

 condensed into independent bodies. After cooling 

 down a little, the glowing ball of the earth was formed 

 out of the gaseous mass, and eventually, as the heat 

 continued to radiate out into space, there was formed 

 at its surface the thin solid crust on which we live. 

 When the temperature at the surface had gone down 

 to a certain point, the water descended upon it from 

 the environing clouds of steam, and thus the first 

 condition was secured for the rise of organic life. 

 Many million years — certainly more than a hundred 

 — have passed since this important process of the 

 formation of water took place, introducing the third 

 section of cosmogony, which we call biogeny, 



III. MONISTIC BIOGENY. 



The third phase of the evolution of the world opens 

 with the advent of organisms on our planet, and 

 continues uninterrupted from that point until the 

 present day. The great problems which this most 

 interesting part of the earth's history suggests to us 

 were still thought insoluble at the beginning of the 

 nineteenth century, or, at least, so difficult that their 

 solution seemed to be extremely remote. Now, at the 



