THE ANDES. 233 



exists, so far as at present known, but one possible, though not very 

 practicable pass. xTo the northward of Lake Argentine, I should estimate 

 the average height of the main range of the Andes, within the limits of 

 the region now under discussion, at nine thousand feet, with many peaks 

 attaining to an altitude of at least half as much more,) In this region, 

 moreover, the continuity of this range is interrupted only by narrow and 

 tortuous river channels, so that in all essential features it has the char- 

 acter of a perfectly continuous mountain range, with an altitude of nine 

 thousand feet, over the summit of which the winds from the Pacific would 

 be forced before reaching the eastern plains. To the southward of Lake 

 Argentine the Andes rapidly diminish in height, and I should not esti- 

 mate the average height of the main range to the south of Lake Mara- 

 villo at above three thousand feet. Moreover, these mountains in this 

 region are interrupted by frequent and, in places, rather broad, low areas, 

 some of which are even beneath the level of the sea and are now occu- 

 pied by broad, open inlets from the Pacific. By a comparison of the 

 different conditions that prevail in the Andes of these two regions, it will 

 readily be seen that the obstacles offered by these mountains to the pas- 

 sage of the winds are very much greater toward the north than to the 

 south of Lake Argentine. These differences in the altitude and topo- 

 graphic peculiarities of the Andes have undoubtedly contributed very 

 largely to produce those different climatic conditions that have already 

 been mentioned as prevailing over the eastern plains region and which 

 led me, at the beginning of the description of the plains, to divide them 

 into the Magellanian region on the south, characterized by a moderate 

 precipitation, and the Santa Cruzian region on the north, characterized 

 by more arid and consequently more sterile conditions. 



Although the Andes to the north and south of Lake Argentine present 

 considerable differences as to altitude and other topographical features, 

 the general character of the climate and vegetation within the region 

 under discussion is remarkably similar throughout and contrasts very 

 strikingly, both as regards the amount of precipitation and the abundance 

 of vegetation, with even the most favored districts of the eastern plains 

 region. In the Narrative of my travels in Patagonia I have already 

 remarked concerning the almost constant rains that prevail throughout 

 the west coast, and the great, almost tropical luxuriance of the Andean 

 forests. Indeed, I believe it is safe to say that in few other parts of the 



