THE PLAINS. 215 



finally ending in the lowermost, which with an average altitude of some 

 three hundred and fifty feet, extends almost uninterruptedly along the 

 entire eastern shore, terminating abruptly in the lofty and precipitous cliffs, 

 which for a thousand miles constitute the predominant feature of this coast 

 s^In addition to the characters described above, there may be mentioned 

 as among the more important features of these plains a series of deep 

 transverse valleys that extend from the Andes to the Atlantic.v These are 

 all true valleys of erosion, and for the most part they are still occupied by 

 considerable 'streams. Over the central interior region, north of the Santa 

 Cruz River, there are extensive lava beds covering hundreds of square 

 miles, while near the mouth of the Rio Gallegos and lying principally 

 south of that stream are other less important lava fields. 



With this general description of the principal topographic, climatic and 

 physical features of Patagonia, as a whole, I shall proceed to a more 

 detailed description of the plains, mountains, transverse and longitudinal 

 valleys, and lake and river systems of the region south of the forty-sixth 

 parallel of south latitude, the only part of Patagonia with which I am per- 

 sonally acquainted and, therefore, able to speak with any authority. 



THE PLAINS. 



Their Geographical Distribution. About one half of the total area of 

 that part of Patagonia now under discussion may be characterized as a 

 plains country, while the same would apply to the northern and eastern 

 portion of Tierra del Fuego, as far south as the Rio Grande on the east 

 coast. The eastern limit of these plains is determined by the Atlantic 

 coast, while the western border is embraced by a widely open curve, com- 

 mencing on the north at the intersection of the forty-sixth parallel and 

 seventy-first meridian. From this point it extends in a very gentle curve 

 to the southwestward as far as the fifty-second parallel. Here, at a little 

 distance beyond the seventy-second meridian, the plains reach their most 

 westerly limits. Beyond the fifty-second parallel the dividing line between 

 the plains and the mountainous region bends sharply to the southeast, 

 crossing the Straits of Magellan and reaching the Atlantic on the east coast 

 of Tierra del Fuego, a little to the southward of the intersection of the 

 fifty-fourth parallel and sixty-seventh meridian. From the above remarks, 

 aided by a reference to the accompanying map, it will be seen that these 

 plains form the lower half of a crescent, stood on end, as it were. 



