Establishment of Vegetation at the surface of the Globe, 71 



waters, absorbed by the power of vegetation, are not fed by 

 springs in proportion to their loss, this marshy soil will by de- 

 grees be dried up, and will be covered in time with fertile mea- 

 dows and trees of all sorts, and will then be fit for cultivation. 



What I have here said with respect to the gradual progress 

 of vegetation is in no degree conjectural : we find its proof at 

 almost every step, as well in the bosom of the earth as at its sur- 

 face, especially in soil which has not been overturned by recent 

 revolutions. In how many places do we not meet, beneath the 

 bed of vegetable or argillaceous earth, ancient peat-bogs ex- 

 tended over strata of sand or heaps of rolled stones ; an evident 

 proof that this soil has formerly been traversed by the waters of 

 rivers, or occupied by those of lakes. The vast marshes of the 

 Somme furnish us with one example among a thousand. The 

 soil is often covered, as M. Girard has observed, with a layer 

 of earth adapted for vegetation, about two feet in its greatest 

 thickness ; the height of the bed of peat on which it rests is from 

 six to ten feet thick between Amiens and Pecquigny; it increas- 

 es to thirty feet opposite the villages of L'Etoile and Long, be- 

 yond which it gradually diminishes. The low part of the city 

 of Amiens, according to the observations of M. Sellier, is built 

 upon a bed of peat, which is sometimes more than twelve feet 

 thick ; it rests upon a bed of marl, which is itself supported by 

 a bed of sand and pebbles, mixed with marine shells. This vast 

 Ibrmation has therefore been long occupied by great lakes, as is 

 proved by the discovery which has been made of several boats 

 and Roman arms preserved in the peat at different depths. 



We are not permitted to follow the establishment of vege- 

 tation in the depths of the ocean ; but if marine plants, like 

 land or fresh-water ones, required to be implanted in an earthy 

 or muddy soil, we should scarcely conceive how they could re-* 

 sist the destructive action of those roaring waves which inces- 

 santly overturn and drive before them every obstacle that comes 

 in their way, sweeps the bottom of the seas, and heaps upon the 

 shores the debris of rocks. To struggle with impediments so 

 powerful, marine plants would require a peculiar mode of ex- 

 istence : nature has therefore awarded them a more solid base 

 than that of a mobile sand, continually tossed about by the im- 

 petuous movements of the waters ; it has fixed their abode 



