- 449 



That vegetables derire their fuflenancc chiefly from air and water, 

 while the portion they receive from the foil is a mere trifle, is a fad 

 often demonftrated ; and that vegetable matters turn upon decay into 

 pure earth, every florift can teftify, who forms his compofl;s of decayed 

 leaves. 



The gardener too throws his weeds and refufe trafli into an heap, 

 that he may bring them back again in two or three years converted 

 into fine mold. 



Since, therefore it appears, that vegetables take little from the foil, 

 and add much to it, I believe we need not look for any other fource 

 whence materials for the repair and renovation of our foil are to be 

 fought. 



Should this mode of forming, and fupplying the fuperficial covering 

 of our earth, be preferred to thofe of Dr. Hutton and Mr. Playfair, 

 it may be unneceflary to proceed any farther in the difcuffion of the 

 Huitonian theory ; as its inventor has no excufe for obtruding a new 

 world upon us, if it appears that the old world is not wearing out ; 

 nor will he eafily find a place to put it in. 



Rivers are, both with Dr. Hutton and Mr. Playfair, the great agents 

 by which the inequalities of our furface are formed, and the mate- 

 rials of our world carried oflF. 



Dr. Hutton, re-echoed by Mr. Playfair (page 351) is pofitive " of 

 " the great fad, that the rivers have in general hollowed out 

 " their vallies." and Dr. Hutton aflerts, page 295, " we never fee a 

 " river in a flood, but we mud acknowledge the carrying away a part 

 « of our land." 



I muft admit, that on thefe occafions, rivers are loaded with adven- 

 titious matter ; but very little of this comes from the original earth ; 

 it is the vegetable foil of pofterior formation, (upon which we have 

 already dwelt fo much) eafily abraded, and eafily repaired, which dif- 

 colour$ the rivers ; this is obvious ia all countries abounding with 



( 3 L ) turf 



