440 



[*•' 



& 



CHAPTER XIX. 



REPRODUCTIVE EFFECTS OF RIVERS continued 



DELTAS FORMED UNDER THE INFLUENCE OF TIDES BASIN AND DELTA OF 



THE MISSISSIPPI ALLUVIAL PLAIN RIVER-BANKS AND BLUFFS CURVES OF 



THE RIVER — NATURAL RAFTS AND SNAGS — MUD-LUMPS NEAR THE MOUTHS AND 

 THEIR PROBABLE ORIGIN — NEW LAKES, AND EFFECTS OF EARTHQUAKES — 

 ANTIQUITY OF THE DELTA — SECTION IN ARTESIAN WELL AT NEW OR- 

 LEANS — DELTA OF THE AMAZONS — DELTA OF THE GANGES AND BRAHMA- 

 POOTRA — HEAD OF THE DELTA AND SUNDERBUNDS— ISLANDS FORMED AND 



DESTROYED — CROCODILES AMOUNT OF FLUVIATILE SEDIMENT IN THE WATER — 



ARTESIAN BORING AT CALCUTTA PROOFS OF SUBSIDENCE— AGE OF THE 



DELTA CONVERGENCE OF DELTAS — ORIGIN OF EXISTING DELTAS NOT CON- 

 TEMPORANEOUS — GROUPING OF STRATA AND STRATIFICATION IN DELTAS 

 CONGLOMERATES — CONSTANT INTERCHANGE OF LAND AND SEA. 



In the last chapter several examples were given of the deltas 

 of inland seas, where the influence of the tides is almost 

 imperceptible. We may next consider those marine or 

 oceanic deltas, where the tides play an efficient part in the 

 dispersion of fluviatile sediment, as in the Gulf of Mexico, 

 where they exert a moderate degree of force, and in the Bay 

 of Bengal, where they are extremely powerful. In regard to 

 estuaries, which Eennel termed ' negative deltas/ they will 

 be treated of more properly when our attention is specially 

 turned to the operations of tides and currents in the 21st, 

 22nd, and 23rd chapters. In this case, instead of the land 

 gaining on the sea at the river's mouth, the tides penetrate 

 far inland beyond the general coast-line. 



BASIN AND DELTA OF THE MISSISSIPPI. 



Extent of the basin.— -The hydro graphical basin of the Mis- 

 sissippi displays, on the grandest scale, the action of running 

 water on the surface of a vast continent. This magnificent 

 river rises nearly in the forty-ninth parallel of north latitude, 

 and flows to the Gulf of Mexico in the twenty-ninth— a 



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