during long continued and heavy rains; but if it should 

 happen to collect in a point at the head of a valley, 

 where the hanks are a little broken away, it is sure 

 to increase the breach, and carry with it much sand 

 or alluvial matter. 



With cultivated grounds, however, the case is ma- 

 terially different ; and, in every instance, where the 

 earth is newly broken up and exposed, it is liable to 

 be carried away, both by wind and rain : every furrow 

 of a corn field becomes a conduit, through the channel 

 of which, the rain waters are conveyed away, satura- 

 ted with alluvion, into larger streams, from thence into 

 creeks, and from creeks into rivers to be wafted down 

 their currents. 



Hence, it will readily be admitted, that the improve- 

 ment and cultivation of districts on the borders of ri- 

 vers, and in the vicinity of their embrochures, will 

 have a tendency, under certain circumstances, to pro- 

 mote the increase and extension of deltas, and to these 

 we may, in a certain degree, attribute their annual 

 gain in an increased ratio. 



To this last however, (viz.) the annual extension 

 of deltas in an increased ratio, Mr. RenneU seems to 

 be opposed, and on the subject of which, and the pro- 

 gressive diminution of the soil of mountains, he makes 

 the following observations. 



" We never fail to remark (says Mr. Rcnnell) on a 

 survey of the naked summits of mountains, that the 

 rain has in a course of ages, washed away the earth 



that covered them ; or, in other words, that there is 



35 



