26 SOUTH AMERICA -THE ANDES EEGIONS. 



of alluvial matter, wliicli represents at the lowest estimate a solid mass 45 square 

 miles in superficial area, with a thickness of over 30 feet. The Mississippi, which 

 discharges four or five times less mud and water, has nevertheless built up in the 

 open sea an alluvial delta terminating in a system of mouths spread out in the 

 marine waters like a branching mass of coral. 



At the mouth of the Amazons the Atlantic has, on the contrary, opened a 

 spacious gulf, and from century to century penetrates farther into the interior of 

 the fluvial valley. The sediment washed down with the stream is not deposited 

 in the gulf, which would else be rapidly filled up ; but it is carried away by the 

 marine current crossing the Atlantic from the Gulf of Guinea to the West Indies, 

 and thus gets lost in the depths of the sea, or else is distributed along the slimy 

 margin of the Guiana seaboard. 



The work of erosion, aided doubtless by a general subsidence of the marine 

 bed, progresses at such a rapid rate that observers have been able to record 

 many indications of its action during the brief period of the last half-century. 

 The shores retreat, so to say, and become indented by new inlets, while the shallow 

 ramifying creeks are transformed to deep channels; the islands and islets slowly 

 melt away until they disappear altogether ; lighthouses erected at some distance 

 from the shore have had to be replaced by others built still farther inland. Owing 

 to this incessant encroachment of the sea on the mainland, the Amazons is esti- 

 mated to have lost from 400 to 500 miles of its former length, and the old beach 

 would now appear to be indicated by the 100-fathoms line. 



The Parnahyba, the Itapicuru and the Tury-assu, former affluents of the main- 

 stream, now reach the sea in independent channels ; the Tocantins, also, which at 

 one time flowed to the Amazons, is now connected with it only by a network of 

 lateral branches, which shift their beds with the periodical floods of the tributary 

 streams. Thus the invasions of the ocean are decomposing the great fluvial basin 

 into secondary systems. Owing to these different oscillations of the seaboard — 

 subsidence on the Atlantic, upheaval on the Pacific side — the whole continent may 

 in a sense be said to have been displaced westwards : it has moved farther from 

 Europe and nearer to Australia. 



III. 



The very nature of the soil and the continental relief are, no less than the 

 vegetation itself, to a large extent the result of the climate, as determined by the 

 prevailing winds, by the rainfall and the running waters fed by it. Thus the 

 Orinoco has cut itself a passage through the northern coast range and the Guiana 

 mountains. In the same way the Amazons has swept away the obstructions to its 

 course, dividing into two sections the whole system of the eastern uplands. In 

 the central parts of the continent, also, the waters, diverging in two opposite 

 directions, have removed all the transverse ridges formerly connecting the Cor- 

 dilleras with the Brazilian highlands. 



To the effects of the climate must also be attributed the gradual contraction 

 and lowering of the Cordilleras themselves in that part of the system exposed to 



