130 



ALLUVIAL DEPOSITES. 



ers. They are, of course, made up of the finest and 

 richest portions of every soil over which the water 

 has passed. We accordingly find such a formation 

 distinguished for its fertihty, as the banks of the 

 Nile, the Mississippi, the Ohio, and the Connecticut. 

 We find a strip of such deposites along the banks of 

 almost every stream, of greater or less width ; also 

 on the shores of lakes and'of the ocean. Swamps 

 also consist of alluvial soil, washed thither by rains 

 and brooks, and generally abound in vegetable mat- 

 ter, which might be employed to great advantage 

 as a manure. 



Alluvial deposites are sometimes stratified, pre- 

 senting distinct layers, wavy, horizontal, or oblique, 

 marlAng successive depositions from water. Mr. 

 Lyell states that " alluvium is strewed alike over 

 inclined and horizontal strata and unstratified rocks ; 

 is most abundant in valleys, but also occurs in high 

 platforms, and even in lofty mountains ; that of the 

 higher grounds usually differing from that found at 

 lower levels." 



It is, however, customary for geological writers 

 to refer beds of gravel, or of stones more or less 

 rounded, that are found in inland districts, as well 

 as the large and detached masses of rock called 

 bowlders or erratic blocks^ to the operation of some 

 great convulsion, by deluges or inundations, more 

 powerful than any causes at present in operation, 

 and to call such deposites diluvium or diluvial depos- 

 ites. It is distinguished from alluvium by the cir- 

 cumstance that it is much coarser, being made of 

 large pebbles or rounded stones, mixed with sand 

 and fragments of every size, often piled up in 

 rounded hills of considerable height, and under such 

 circumstances as would preclude the possibility of 

 its resulting from existing streams. We find it 

 covering the highest mountains and spread over 

 every kind of rock ; in short, so disposed as to 

 prove very conclusively that at some former period 



