136 FIRST FORMS OF VEGETATION. 
particles of sand into which they crumble its sur- 
face, and their own decaying tissues, a thin layer. 
of mould fit for the reception of the simplest 
mosses. These in their turn, add their contribu- 
tion of withered leaves, and increase the film of 
soil; others of a larger growth supplying their 
places, and running themselves the same round of 
growth and decay. Plants of a higher and yet 
higher order gradually succeed each other, each 
series binding together, and preparing for the 
growth of its own species or of others, the loose 
and incoherent mass of decaying tissues, sand, 
and disintegrated soil which the previous oc- 
cupants had left behind them. At length the 
rock, once as bleak and desolate as though it had 
been vomited from the depths of some vast vol- 
cano, and on whose surface the smallest wild- 
flower could not find a resting-place for its tiny 
root, becomes a verdant meadow fit to support a 
host of animals; a rich garden of beautiful flowers 
smiling in the sunshine; or a wide expanse of 
noble forest waving its billowy foliage in the pass- 
ing breeze. 
* Seeds to our eye invisible can find 
On the rude rock the bed that fits their kind ; 
There in the rugged soil they safely dwell, 
Till showers and snows the subtle atoms swell, 
And spread th’ enduring foliage ; then we trace 
The freckled flower upon the flinty base ; 
