269 



such circumstances, the alluvion of rivers is rendered, 

 in some degree, tributary to the formation of deltas ; 

 but it is comparatively less, in relation to the Po > the 

 Indus, the Nile, &c. than thnt occasioned, 2dly, hy 

 the improvement and cultivation of lands, and also 

 by the existence of sandy deserts in the vicinity of 

 such deltas. 



The improvement and cultivation of lands, in al- 

 mot all situations, on the borders of rivers, and at 

 their mouths, renders the soil peculiarly liable to be 

 carried away, both by rains and wind, into the rivers 

 or sea ; which tends greatly to the increase of allu- 

 vion, and the formation of sand bars, banks, and 

 deltas ; the latter in particular is a powerful agent in 

 this business, though but seldom, or but little attended 

 to. Indeed the phenomena of winds, as they relate 

 to this subject, seem not to have received that degree 

 of attention which they justly merit, and which is re- 

 quired by every principle of truth and sound philoso- 

 phy. But a little attention and observation will sooii 

 convince any person, susceptible of conviction, that 

 the same phenomena accompany the winds, or currents 

 of air, as do currents of water. If the current of a 

 river flow majestically along, though at the rate of 

 four or five miles in an hour, not a grain of sand is dis- 

 turbed or lifted from the bottom ; for the current of 

 water is often so clear, that we may see to the depth of 

 one and even two fathoms ; nay, it is said from eight 

 to ten fathoms in a clear day. If we trace up its 

 auxiliary branches, even to the smallest brooks^ we 



