6 SOUTH AMEEICA— THE ANDES EEGIONS. 



Geolo"-ists who liave studied the contours and general incline of these inland 

 reo-ions find that the movement of waters has been developed in two principal 

 directions, one parallel with the meridian, and indicated chiefly by the trend of 

 the Parao-uay and of the Parana, the other intersecting the first at right angles, 

 and flowino- from the Andes to the Atlantic. The Amazons, a " liquid equator," 

 as it has been called, follows the main axis of this second hydrographie system. 

 The aspect presented by the semicircle of the Andes bc^tween the Bogota and 

 Bolivian plateaux attests the vast work of erosion that has been accomplished 

 in this upland region. The eastern slope of the Cordilleras has evidently been 

 eaten away by the running waters to an enormous extent ; numerous lateral ridges 

 have been entirely levelled, and their triturated debris has been distributed by 

 the streams over the beds of great inland seas, which at one time occupied the 

 central reo-ion of the continent. The sedimentary matter thus carried down 

 towards the fluvial estuaries was regarded by Humboldt as of old red sandstone 

 origin, while Martins attributed it to triassic formations. . But in reality these 

 deposits are comparatively recent quaternary clays and sands, and according to 

 Agassiz are partly of glacial origin. 



The part of the Andean system that has best resisted the fluvial action is the 

 huge mass of the Bolivian uplands. This central fortress of the South American 

 rampart is no less than 500 miles broad between the escarpments which plunge 

 into the waters of the Pacific and the eastern plains still roamed by the nomad 

 Indians ; but a little farther north, in the very axis of the Amazons, under 3° 

 south latitude, the main range of the Cordilleras is reduced to a thickness of 

 scarcely more than 120 miles. 



East of Bolivia the headstreams, which trend some to the Amazons, some to 

 the Paraguay basin, have not been strong enough to sweep away the Andean 

 foothills. Along the parting-line the expanse of level plains intervening between 

 the paleozoic Andean rocks and those of the Brazilian plateaux has a normal 

 breadth of no more than 250 miles ; towards the centre it is studded with nume- 

 rous hills and isolated ridges, surviving witnesses of the crystalline nucleus and 

 other formations which at one time occupied the whole continent from sea to sea. 

 The passages which the Amazons and the Orinoco have had to cut for themselves 

 through the coast ranges are much narrower still than this central depression. 

 Between the Tapajoz and Xingu mouths the Amazons valley is scarcely GO miles 

 broad from hill to hill. 



Forests and Habitable Lands. 

 The enormous excess of pluvial waters which distinguishes the southern 

 continent, and which has created this astonishing system of ramifying streams, 

 has, however, conferred little more than a nominal advantage on its inhabitants, 

 at least in the equatorial zone. Such liquid masses are too copious, too irregular 

 in their regime to be controlled by man, who till recently has scarcely been 

 able to utilise them even for navigation. Moreover, the tepid and oppressive 

 climiate has hitherto been opposed to the acclimatisation of the while and half- 



