DARWINISM AND EVOLUTION 181 



origin and becoming of the earth's material and external 

 features as we now know them. Accepting from astro- 

 nomy the notion of our planet's primary condition as a 

 cooling sphere of incandescent matter, it goes on to 

 show how the two great envelopes, atmospheric and 

 oceanic, gaseous and liquid, have gradually formed 

 around its solid core ; how the hard crust of the central 

 mass has been wrinkled and corrugated into mountain 

 chain and deep-cut valley, uplifted here into elevated 

 table-land or there depressed into hollow ocean bed ; 

 how sediment has slowly gathered on the floor of the 

 sea, and how volcanic energies or lateral pressure have 

 subsequently forced up the resulting deposits into Alpine 

 peaks and massive continents. In this direction, it was 

 Lyell who principally introduced into science the uni- 

 formitarian or evolutionary principle, who substituted 

 for the frequent cataclysms and fresh beginnings of the 

 earlier geologists the grand conception of continuous 

 action, producing from comparatively infinitesimal but 

 cumulative causes effects which at last attain by accretion 

 the most colossal proportions. 



Here biology next steps in, with its splendid ex- 

 planation of organic life, as due essentially to the 

 secondary action of radiated solar energy on the outer 

 crust of such a cooling and evolving planet. Falling 

 on the cells of the simplest green plants, the potent 

 sunlight dissociates the carbon from the oxygen in the 

 carbonic acid floating in the atmosphere, and builds it 

 up with the hydrogen of water in the tissues of the 

 organism into starches and other organic products, 

 which differ from the inert substances around them, 

 mainly by the possession of locked-up solar energy. On 



