assisted by the growth of vegetables: the former of 

 which it carefully observed and particularly examin- 

 ed, together with the operations of currents, it may be 

 asserted with safety, that there is not a spit, sand bar, 

 sand-bank, flat, or alluvial island, the formation, mo- 

 dification, or changes of which may not be accounted 

 for, by the operation of one or the other of these agents, 

 either separately or combined. This, however impro- 

 bable and unimportant it may appear, is of the utmost 

 consequence in all hydraulic researches, and particu- 

 larly in military architecture, where it becomes neces- 

 sary to erect fortifications on the borders of alluvial 

 districts, or in situations liable to changes. 



The process by which alluvial banks are more and 

 more elevated by Vegetation, and more especially by 

 winds, is nearly as follows 



When a newly formed bank or banks, are elevated 

 by successive deposites of alluvion, to the height at 

 which the annual inundations of the waters rise, they 

 are, on the subsidence of the waters, left exposed to the 

 operations of the winds, which, however small the 

 elevation may be above the water, will soon produce 

 some change ; for the wind in passing over an uni- 

 form surface, as that of a river, lake, &c. and meet- 

 ing with an obstruction, is elevated in the same 

 manner as the current of water in a rivulet, where 

 it meets with an obstruction in its course. If the 

 wind be so strong as to raise the sand, when it first 

 meets the obstruction, or strikes this sand bank, it is 

 carried over and at a little distance beyond the sum- 

 mit of the bank, before it is let fall, on the opposite 



