368 



Hence it is, that we have sand bars, or alluvial for- 

 mations below projecting points of land ; at, or near, 

 and below the entrance of one river into another.* 



As soon as the current of a river receives the check 

 of a strong and high tide, the sandy particles, how- 

 ever little or great the quantity, are deposited at the 

 bottom ; hence, it may be presumed, we have no 

 deltas at the mouths of all our northern rivers, where 

 the tides are strong and rise high. 



Here again I have the support of Mr. Rennell, who 

 sometimes advances an opinion at variance with the 

 theory which he is endeavouring to support. 



Speaking of the deltas of rivers he says, " Which 

 rivers, having brought down with their floods, vast 

 quantities of mud and sand from the upper lands, de- 

 posite them in the lowest place in the sea ; at whose 

 margin the current which has hitherto impelled them, 

 ceasing, they are deposited by the mere action of 

 gravity."^ 



With rivers, on the contrary, however large or 

 smalL that fall into deep bays or gulfs, where there 

 are but little or no tides to check the force of their cur- 

 rents, as with the Mississippi, and the several rivers in 

 the Gulf of Mexico ; the ^Nile, the Po, and other rivers 

 that are disharged into the Mediterranean sea, the case 

 is materially different, and it will be admitted that under 



* See Lewis and Clarke's Travels up the Missouri, 

 t ReiincU'b Herodotus, page 484. 



