214 PATAGONIAN EXPEDITIONS: GEOGRAPHY. 



continual rains, while over the higher peaks and ranges snowstorms 

 prevail almost constantly, resulting in the accumulation of vast fields of 

 snow and ice, which in turn give origin to numerous glaciers. Owing to 

 the abundant precipitation the lower slopes of the mountains support 

 dense forests, which along the channels of the west coast, attain to an 

 almost tropical luxuriance. Along the eastern slopes of these mountains 

 there is a chain of lakes, which for numbers, size and beauty, are unsur- 

 passed elsewhere by any similar series of mountain lakes. To the 

 eastward, on a line approximating that of the seventy-second meridian, 

 the mountains terminate rather abruptly, and the country assumes the 

 appearance of a rather high plateau or plain, with an altitude at the base 

 of the mountains averaging perhaps three thousand feet. Here begin the 

 plains of eastern Patagonia. Their semi-arid and barren nature contrasts 

 strongly with the abundant rainfall and dense forests of the Andes, dis- 

 tant less than one hundred miles. It is easily explained, however, and 

 is a result of the peculiar topography of the region. The prevailing 

 southwesterly winds, during their long journey across the south Pacific, 

 become thoroughly saturated with moisture, and in this condition they 

 reach the west coast of Patagonia and are forced up the western slopes 

 and over the summits of the Andes. The continuously lower tem- 

 peratures, to which they are subjected during their passage over the 

 mountains, cause the condensation of the contained moisture and result 

 in the really enormous precipitation, which, as we have already noticed, 

 falls as rain over the lower slopes and as snow at the summit of the moun- 

 tains. In this manner the atmosphere is as completely deprived of its 

 moisture during its passage over the Andes as a water-soaked blanket, 

 when passed through the most improved modern wringer, and in this 

 desiccated condition the winds descend upon the eastern plains in a state 

 calculated to extract rather than impart the much needed moisture to 

 the soil, so that the latter remain in their present semi-arid and barren 

 condition. 



While the Patagonian plains have an altitude of some three thousand 

 feet at the base of the Andes, they slope very gently to the eastward, and 

 at a distance of some fifty miles from the Atlantic coast, their elevation is 

 more rapidly decreased by a series of escarpments or terrace-like slopes, 

 which face to the eastward and terminate a succession of level plains, 

 decreasing in altitude as one passes from the interior to the coast and 



