GEOLOGICAL DIVISIONS. 21/ 



Nevertheless, where the sandhills spread over a district liable to 

 be flooded they must influence the sedimentation of mud carried 

 by the water, and may ultimately by its gradual accumulation give 

 rise to a closed impermeable basin, lam inclined to think that an 

 influence of this sort has been at work in the formation of the small 

 perennial ponds or (i nawars ; " for both of those which I saw are 

 surrounded by sand dunes. 



In addition to these alluvial and aeolian deposits there are other 



Recent volcanic form- recent formations of volcanic origin. These 



atlons - consist of various accumulations of lavas and 



cinders, and also the deposits of mineral springs which have 



produced large masses of travertine. They will be described in a 



separate chapter. 



( 39 ) 



