I. Bowman — Physiography of the Central Andes. 203 



Between the two great Andine tablelands and their super- 

 imposed peaks and ranges is the central basin or plateau of 

 lower altitude than the bordering highlands, separated 

 from the latter by the two great roughly-parallel scarps of 

 marked rectilinear quality often for long distances. This is 

 the alti-plano or " planicie " of Bolivia. It is without outlet 

 to the sea, an interior drainage basin, and therefore technically* 

 a part of the true desert area of the world. On the north 

 the bordering scarps converge in latitude li° south, enclosing 

 Lake Titicaca, whose waters discharge by way of the Desa- 

 guadero river into Lake Poopo, only to be discharged in turn 

 into the Salar de Coipasa and the adjacent salars to the south. 

 Here and there the otherwise fiat basin floor is broken by 

 piles of volcanic detritus, lava flows from occasional centers of 

 igneous activity, as the Isla de Panza, of Poopo ; or by ancient 

 and highly crumpled sedimentaries, as where the upturned 

 edges of slates and quartzites rib the hills back of the port 

 of Desaguadero. East of the central Andes, as indeed along 

 the whole eastern front of the Andine Cordillera, from the 

 Argentine pampas to the llanos of Venezuela, the dissection of 

 the adjacent highlands has been accompanied by the formation 

 of extensive piedmont deposits. The western plateau descends 

 by a relatively smooth slope to the coastal deserts of Tara- 

 paca and Atacama. Between these deserts and the Pacific 

 shore are low mountain ranges of complex geologic and physio- 

 graphic character, the coast ranges of Chili and Peru, 



With this general statement of the lie of the land and its 

 principal topographic outlines, we shall next consider current 

 explanations and then the more technical aspects of the physi- 

 ography, the genesis and development through time, of the 

 principal topographic and drainage features. 



All of the older and most of the newer descriptive text-books 

 of geography describe the western Andes as a majestic line of 

 lofty volcanoes with deep abysses and precipitous walls and 

 canyons, a stupendous volcanic pile rising sheer from the sea. 

 This conception was natural to the text-book writer reading 

 the traveler's account of lofty Chimborazo, whose white summit 

 (21,000 ft.) is visible on clear clays from the gulf of Guayaquil ; 

 or of El Misti, with 11,000 ft. of relative altitude, at Arequipa, 

 Peru. True it is that in the south, where the Patagonian 

 Andes terminate this great orographic system, there is a 

 mountain-bordered shore which for scenic grandeur meets thp 

 expectations of the liveliest imagination. But the peaks are here 

 not volcanic cones and the absolute altitudes fall far short of those 



*Dr. John Murray, Origin and Character of the Sahara, Science, vol. xvi, 

 p. 106, 1890. 



