416 



XVIII. 



REPRODUCTIVE EFFECTS OF RIVERS. 



LAKE DELTAS GROWTH OF THE DELTA OF THE UPPER RHONE IX THE LAKE 



OF GENEVA PLAYFAIR ON THE ORIGIN OF LAKE-BASINS — COMPUTATION OF 



THE AGE OF DELTAS RECENT DEPOSITS IN LAKE SUPERIOR DELTAS OF 



INLAND SEAS COURSE OF THE PO ARTIFICIAL EMBANKMENTS OF THE PO 



AND ADIGE DELTA OF THE PO, AND OTHER RIVERS ENTERING THE ADRI- 



ATIC — RAPID CONVERSION OF THE GULF INTO LAND — MINERAL CHARACTERS 



OF THE NEW DEPOSITS MARINE DELTA OF THE RHONE — VARIOUS PROOFS 



OF ITS INCREASE STONY NATURE OF ITS DEPOSITS —COAST OF ASIA MINOR 



•DELTA OF THE NILE — CHRONOLOGICAL COMPUTATION OF THE GROWTH 

 OF THE NILE MUD AT MEMPHIS. 



DELTAS IX LAKES. 



the fourteenth chapter of the 



I have already spoken in 

 action of running water, and of the denuding power of rivers, 

 but we can only form a just conception of the excavating 

 and removing force exerted by such bodies of water, when 

 we have the advantage of examining the reproductive effects 

 of the same agents : in other words, of beholding in a palpable 

 form the aggregate amount of matter, which they have 

 thrown down at certain points in their alluvial plains, or m 

 the basins of lakes and seas. Yet it will appear when we 

 consider the action of currents, that the growth of deltas 

 affords a very inadequate standard by which to measure tie 

 entire carrying power of running water, since a consideraole 

 portion of fluviatile sediment is swept far out to sea. 



Deltas may be divided into, first, those which are formed 

 in lakes ; secondly, those in inland seas, where the tides are 

 almost imperceptible ; and, thirdly, those on the borders 01 

 the ocean. The most characteristic distinction between the 

 lacustrine and marine deltas consists in the nature ot tlie 

 organic remains which become imbedded in their deposits , 



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