80 Evolution of the Earth. 



grass, Ixerbs ami trees, and peopled it with a myriad forms 

 of life, giving all to luau as the crowning glory of creation, in- 

 to whose nostrils he had breathed the breath of life. The Gen- 

 esis story is a simple, graphic and suggestive legend, which, 

 when we have ceased to regard it as a statement of scientihc; 

 tnith, Ave would by no means exjiunge from the sacred lit- 

 erature of the world. It contains some hints of man's prim- 

 itive conception of cosmogony, some theory, crude and im- 

 perfect as it is, of the way in which life began in the world; 

 but there is not even a suggestion in it of this wonderful 

 story of geology about which we are to think to-night. 

 The visible heavens, and the surface of the earth 

 were known to man in those earlier days ; but of what 

 lay within the bosom of the earth, of the forces which had 

 upheaved its mountains, excavated its valleys, prepared it 

 for the teeming life which he beheld around him, he knew 

 practically nothing. The sky to him was a solid firmament ; 

 above it, perhaps, the heaven of his imagination, the home 

 of his gods. Beneath the earth was the subterranean abode 

 of the dead, out of which conception the observation of the 

 lurid fires and destructive energy of volcanoes naturally 

 helped him subsequently to evolve the notion of a fiery 

 hell. 



To the modern mind all this is changed, as by the touch 

 of a magician's wand. Where, indeed, can we find a magi- 

 cian as potent as Star-eyed Science, which transforms the 

 misty nebulse into suns and galaxies, and the rocks beneath 

 our feet into pages of sublimest history ? Let us now turn 

 to the study of these pages, writ all over with stories of the 

 past, and trace therein as well as we may, in the brief time 

 allotted to us, the history of the earth. 



Primitive ConditiojSt of the Earth's Surface. When 

 the surface of the globe had parted with its heat sufficiently 

 to allow the vapors of the atmosphere to condense and de- 

 scend in rain, it had already become somewhat less homo- 

 geneous in form and structure than it was in its original 

 heated condition. The solid crust had become differentiated 

 from the fiery core. Cooling was accompanied by contrac- 

 tion, which produced inequalities of altitude, though less 

 marked than those presented by our present mountain 

 ranges. Relatively to present conditions, the solid portion of 

 the earth's surface may be said to have presented a homo- 

 geneous structure. There was no soil, capable of sustaining 



