454 



To return to our rivers ; fmce it appears that the depredations they 

 commit on their banks, are unimportant, let us try them in a vertical 

 direction, and fee, if in their channels and bottoms, they are invad- 

 ing and carrying off the world. 



Mr. Playfair calls rivers, lines deeply engraved on the furface of the 

 earth ; I by no means admit this account of them, for where they run 

 through plains, not alluvial, the river feldom is funk more than a 

 very few feet below the furface, and this is all the depth it has reached, 

 fmce the beginning of the world: in alluvial plains they are perpetu- 

 ally changing their channels, cutting out new ones, and filling up the 

 old ; but this cofls the world nothing, the river is afting upon its 

 own depofits, carrying them off, and replacing them ad libitum, from 

 the detritus of our foil, and this at a level above the original earth. 



The reafon why thefe lines are not deeper, is obvious; the bottom 

 of the river, from its fource to the fea, is covered with adventitious matter, 

 ftones, gravel, fand, mud, over thefe, without further invafion of the world, 

 our river, like Horace's, 



Labitur, et labctur in omne volubllis sevum. 



That rivers in floods carry down with them vail quantities of mud, 

 &c. cannot be denied, it remains to examine what becomes of it : the 

 firfl; depofit of the coarfeft materials are made on the alluvial platforms, 

 which abound in moft rivers ; Mr. Playfair calls them haughs ; in the 

 north of Ireland they are ftiled homes; thefe (by his own admifllonj 

 are found to be raifed far above the level the river once ran at, a 

 fa£l fimple in itfelf, and eafily accounted for; but fo contrary to Mr. 

 Playfair's fyftem of perpetual excavation, that to get over the difficulty, 

 he is obliged to ajfume that rivers, in their original form, were a fuc- 

 ceflion of lakes and cataraBs, 



The principal confumption of the materials carried down by our ri- 

 vers, is in the formation of alluvial land at their mouth, and the pro- 

 longation of our continents: ftill, however, we muft admit that much 



is 



