40 THE HARMONIES OF NATURE. 



slope of the river's bed is lessened. It not unfrequently hap- 

 pens, that two large rivers after their junction have only the 

 surface which one of them had previously ; and even in some 

 cases their united waters are confined in a narrower bed than 

 each of them filled before. By this beautiful adjustment, the 

 water which drains the interior country is made continually to 

 occupy less room as it approaches the sea, and thus the most 

 valuable part of our continents the rich deltas and great 

 alluvial plains are prevented from being constantly under 

 water.* 



The inequalities of the earth's surface, the elevation of vast 

 tracts of country many thousand feet above the level of the sea, 

 and the deep valleys which the torrents have gradually scooped 

 out in the flanks of the mountains, are also prominent causes of 

 that wonderful variety of climate which gives birth to a no less 

 wonderful variety of plants and animals. 



Fancy the mountains brought down to the level of a uniform 

 plane ; no peaks soaring aloft into the regions of perpetual snow, 

 no declivities leading the wanderer in a few hours from Arctic 

 coldness to the genial mildness of an Italian sky; no precipitous 

 streams, whose foaming waters as they bound along first reflect 

 the dark pine in their crystal mirror, then the sturdy oak, and 

 finally the noble chestnut or the graceful laurel ; and then how 

 monotonous would be the landscape, how uniform the character 

 of organic life over vast tracts of country where now vegetation, 

 thanks to the perpetual changes of elevation and aspect of the 

 soil on which it grows, is seen revelling in an endless multipli- 

 city of forms. 



The actual distribution of sea and land over the surface of the 

 globe is likewise of the highest importance to the present condi- 

 tion of organic life. If the ocean were considerably smaller, or if 

 Asia and America were concentrated within the tropics, the tides, 

 the oceanic currents, and the meteorological phenomena on which 

 the existence of the vegetable and animal kingdoms depend, 

 would be so profoundly modified, that it is extremely doubtful 

 whether man could have existed, and absolutely certain that he 

 could never have risen to a high degree of civilisation. 



The dependence of human progress upon the existing configu- 



* Sir Charles Lyell's Principles of Geology. 



