RECORDti OF MEETINGS 289 



B. L. Miller, Geological Obseevations iisr the Andes of Peru and 

 Bolivia. 



SUMMAKY OF PaPEE 



Professor Miller stated that the South American Continent contains 

 three great areas of highlands known as the Highlands of Guiana, the 

 Brazilian Highlands, -and the Andes Mountains. The first two corre- 

 spond in a general way to the highlands of eastern Canada and the 

 eastern United States, in that they consist largely of metamorphic rocks 

 of Pre-cambrian or Early Paleozoic age, and represent mainly the roots 

 of once high mountains now reduced by erosion to hills and mountains 

 of moderate height, while the Andes are to be compared with the Cor- 

 dillera of the western ISTorth America in that they are composed, for the 

 greater part, of sedimentary rocks of Cretaceous and Tertiary age, into 

 which have been intruded great masses of andesites, trachytes, rhyolites, 

 and other igneous rocks, while active or recently extinct volcanoes con- 

 stitute some of the greatest elevations. A more careful comparison of 

 the Cordillera of JSTorth and South America brings out several distinc- 

 tions. In the northern continent the western mountains form several 

 discontinuous ranges which extend from east to west over a wide range 

 of territory from central Colorado to the Pacific Ocean, while the Cor- 

 dillera of South America extend uninterruptedly from Colombia to Tierra 

 del Fuego, and are so concentrated that nowhere is the entire width more 

 than a few hundred miles, and in many places it is scarcely more than a 

 hundred miles from the shores of the Pacific Ocean to the eastern flank 

 of the Andes mountains, where the great interior plains begin. Not- 

 withstanding the compactness and continuity of the Cordillera of South 

 America they are by no means a unit, but in the character of the rocks 

 of which they are composed and in the uplifts to which they have been 

 subjected they exliibit much variety and complexity. The topographic 

 features of western South America consist of the following divisions, 

 named in order from the Pacific Ocean eastward : (1) the Coastal Eange, 

 (3) the Longitudinal Valley, (3) the Maritime Andes or the Cordillera 

 Occidental, (4) the Interior Plateau, Altiplanicie, or Bolivian Plateau, 



(5) the Eastern Andes, Cordillera Oriental, or Cordillera Peal, and 



(6) the great Interior Plains. 



All of the different ranges of the Andes are of primary importance 

 on account of the mineral resources which they contain. In the coast 

 ranges are numerous deposits of gold, silver and iron; in the Longitudi- 

 nal Valley are the great deposits of sodium nitrate and considerable 



