Geology and Mineral Resources of Paraguay A Reconnaissance

6 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYmate airline distances from Asuncion, the capital city,to capitals of neighboring countries are as follows:Miles KilometersBuenos Aires, Argentina ___________________ 650 L, 050La Paz, Bolivia___________________________ 610 980Lima, Peru_ _______________________________ 1,000 1, 610Montevideo, Uruguay_______ ________________ 650 1, 050Rio de Janeiro, Brazil-______________________ 920 1,480Santiago, Chile_____________________________ 1, 100 1,770TOPOGRAPHY AND DRAINAGEThe entire country is one of low relief (pi. 1), withaltitudes ranging from 55 meters above sea level at thejunction of the Rio Paraguay and Rio Alto Parana toan extreme of 700 meters on one peak just east ofVillarrica.There is, however, a marked difference in the topographyon the two sides of the Rio Paraguay, whichbisects the country along a north-south line. Thatportion east of the river, called Paraguay Oriental, isgently rolling to hilly, with nearly level valleys. Someof the relatively low hills and mountains occur in ratherdistinct chains. Made up in large part of soft sedimentaryrocks or of deeply weathered basalt, the hillsare being degraded by erosion processes and presentlow rounded outline in most places. Here and there,however, where there are outcrops of harder sedimentaryor igneous rocks, they have more rugged shapesand present bits of spectacular scenery, albeit on arather small scale.The Chaco Boreal on the western side of the RioParaguay, the Paraguayan part of the Gran Chaco, isa vast aggrading alluvial plain that rises almost imperceptiblywestward from the river toward the foothillsof the Andes not far within the Bolivian border. Themonotony of this nearly level, poorly drained plain(see fig. 2) is broken only in its most northern part,where there are a few good-sized hills, both in Paraguayand in Bolivia, that mark places where islands of bedrockprotrude above the thick alluvium.Virtually all of Paraguay lies within the great drainagebasin of the Rio Parana, which also drains appreciableparts of Bolivia, Brazil, Argentina, and Uruguayand empties into the estuarine Rio de la Plata, aboveBuenos Aires. A few maps show a small area in theextreme northwest corner of Paraguay as drained bythe Amazon, but the weight of existing evidence isthat the entire country lies within the Parana basinand it is so shown on plate 1.The true Rio Parana heads at the southern tip ofParaguay at the junction of its two main branches, theParaguay and the Alto Parana. The Rio Paraguay isthe larger of these two and is the main avenue of drainageand of river commerce in the country. It heads inMato Grosso, Brazil, and trends nearly due south. ItFIGUKE 2. Typical terrain and vegetation in the Gran Chaco. View about 30 kilometers west of Puerto Casado.