S MODERN POBfiST ECONOMY. 



men and browsing quadrupeds. When these requisites 

 are secured, the hardest rock is as certain to be overgrown 

 with wood as the most fertile plain, though in drier 

 seasons the process is slower in the former than in the 

 latter case. Lichens and mosses first prepare the way for 

 a more highly organised vegetation, They retain the 

 moisture of rains and dews, and bring it to act, in com- 

 bination with the gases evolved by their organic processes, 

 in decomposing the surface of the rock they cover; they 

 arrest and confine the dust which the wind scatters over 

 them, and their final decay adds new material to the soil 

 already half-formed beneath and upon them. A very thin 

 stratum of mould is sufficient for the germination of seeds 

 of the hardy evergreens and the birches, the roots of which 

 are often found in immediate contact with the rock, sup- 

 plying their trees with nourishment from a soil deepened 

 and enriched from the decomposition of their foliage, or 

 sending out long rootlets into the surrounding earth in 

 search of juices to feed them.' 



The light which has been thrown by Darwin and others, 

 who have followed in the track of research opened up by 

 him, upon the phenomena of a struggle for life and the 

 survival of the fittest, which is going on extensively in 

 nature, enables us to account satisfactorily for the great 

 extension of forests over Europe and over other lands in 

 which forests predominate. We can see how it may have 

 been brought about, and not only see how ligneous vege- 

 tables should have superseded herbs, but understand how 

 these have superseded lichens, and fruitful fields have super- 

 seded forests. In the case of the lichen-covered rock each 

 succeeding plant found a soil and condition more favour- 

 able for its growth than for the growth of the plant by 

 which it was preceded ; and this made way for it after it had 

 served its generation according to the will of God. By a 

 similar process was the soil subsequently prepared for the 

 production of trees, which, in common with their imme- 

 diate predecessors, could not have flourished at an earlier 



