286 GENERAL VIEWS, 



distinction, that in the last case the phenomena succeed 

 by almost impercep f ible gradations, while they crowd 

 upon and follow each other in rapid succession on the 

 ascent of mountains. The height of 4 or 5000 yards 

 in the hottest parts of the globe, produces changes as 

 distinct as the 2000 leagues or more, which lie between 

 the Equator and the polar regions. The three causes 

 of the influence of which we have just spoken, all re- 

 appear within this space ; the heat is diminished, the 

 air is dry, and the duration of light is protracted. Te 

 these we must add two others ; a decrease of depth in 

 the volume of the air, and a scarcity of those substan- 

 ces which abound in carbon, and are produced by the 

 decomposition of organic bodies. 



Many of the less perfect plants grow under circumstan- 

 ces the most unfavourable to vegetation. Neither the 

 total privation or the excess of light, nor the extremes 

 of moisture or dryness, nor scorching heat or the fierc- 

 est cold, nor want of mould or scantiness of carbon, 

 prevent these rude species from developing their 

 forms ; neither are they of small importance in the ge- 

 neral economy of nature. By them the soil is prepar- 

 ed, and they lay the foundation of vegetation. 



The rudest of the Lichens, mere coloured crusts of 

 the simplest structure, first fix themselves on the smooth 

 surface of the rock which they erode, break up, and 

 scoop into hollows. These at last are turned into dust. 

 Sorts a degree higher in the scale of organization, to- 

 gether with some elegantly formed Mosees, resembling 

 trees and shrubs in miniature, take their place. By 

 the successive dissolution and regeneration of such ve- 

 getation through a long series of years, a thin stratum 

 of mould is formed upon the stone, in which Herbs and 

 Grasses take root and grow. Generations succeed each 



