62 DEBRIS. 



These plants grow, and after their death, either in 

 part or wholly, leave a debris which becomes profit- 

 able to succeeding generations of vegetables. Or- 

 ganic matter accumulates in the course of ages, 

 even in the most ungrateful soils, in this way, and 

 by these repeated additions they become less and 

 less sterile. It is probable that the virgin forests of 

 the New World have thus supplied the wonderful 

 quantity of vegetable mould in which the present 

 generation of trees is rooted. At Larega de Supia, 

 in South America, the slipping of a porphyritic 

 mountain covered completely with its debris, to the 

 extent of nearly half a league, the rich plantations 

 of sugar-cane which were there established. Ten 

 years afterwards I saw the blocks of porphyry shad- 

 owed by thick groves of mimosas ; and the time, 

 perchance, is not very remote when this new forest 

 will be cleared away, and the strong soil, enriched 

 with its spoils, will be restored to the husbandman. 

 " The chemical composition of the earth adapted 

 for vegetation must of course participate in the 

 nature of the rocks and substrata from which it was 

 derived ; and the elements which enter into the 

 constitution of mineral species ought to be found 

 in the soils, which, by the effect of time or human 

 industry, may serve for the re23roduction of vegeta- 

 bles. It is on this account that it becomes inter- 

 esting to study the composition of the minerals, 

 which are the most abundantly dispersed in the 

 solid mass of the globe." 



