2S& 



than half the year, sweeping over these heated wastes, 

 and raising the sand in clouds, and bearing it across 

 the gulf of Scindy, and the mouth of the Indus, need 

 we question the sources from which the materials were 

 derived to form those deltas ? 



If we add to this the labours of man, upon these 

 new forming districts, in dyking, and raising mounds, 

 or oilier obstructions to the winds thus charged, need 

 we, or can we pretend, that the alluvion of rivers is 

 the source by which these deltas were formed and ex- 

 tended, and that too in an increased ratio annually ? 

 I presume not, and for a very obvious reason : Mr. 

 Rennell observes, that "The mean rate of motion of 

 the Ganges, is less than throe miles an hour in the dry 

 months."* That of the Indus, and also the Booram- 

 pooter,f is nearly the same. 



This, it must appear evident, is by no means suffi- 

 cient to bear up and convey sand to any considerable 

 distance. And as it is but once a year, and that, 

 *< during the wet season, and whilst the waters are 

 draining off from the in-undated lands/' the cur-* 

 rents are accelerated in any considerable degree, we 

 may reasonably conclude, that the alluvion derived 

 from this source is comparatively small, to that which 

 is supplied from the other two sources, (viz.) the direct 

 or indirect labours of man, and the operations of winds, 

 &c. on the cultivated grounds, and deserts, in the vici- 

 nity of deltas. 



* Rennell's Map, p. 34-0. t Philosophical Transactions for 1781. 





