50 GEOGRA I'JIK ' FE. I TUBES OF SO UTHERX P. 1 TA G OXIA 



Since Dr Moreno's paper is doubtless easily accessible, I shall not 

 attempt a detailed description of this interesting region, but shall 

 briefly discuss the factors which have contributed to produce the 

 existing unusual drainage conditions. I am the more easily impelled 

 to this course, since some of the theories advanced by Dr Moreno in 

 explanation of certain features described b}'^ him appear to me un- 

 tenable. .\t any rate, they are not supported by most of the observa- 

 tions made by myself during the past three years. 



A study of the southern Andes at any j^oint reveals the fiict that 

 they are composed of three distinct, parallel ranges, separated by two 

 dee|), narrow, longitudinal valleys. The middle of the three ranges 

 is everywhere much higher than the two lateral ranges and may be 

 reckoned as the principal range of the Andes. The western lateral 

 range is at present partially submerged beneath the Pacific, but is 

 still distinctly seen in the chain of islands extending all along the 

 western coast. The western of tlie two longitudinal valleys is at 

 present throughout the greater extent of Patagonia entirely sub- 

 merged beneath the sea and is now represented by the narrow sys- 

 tem of rather deep channels that separates the islands from the main 

 land and offers an almost continuously navigal)le iidand waterway 

 extending from the southernmost point of the Brunswick Peninsula 

 to the 42(1 parallel of south latitude, or throughout more than twelve 

 degrees, a distance of over 700 miles. 



The eastern lateral range of the Andes is seen in the foothills that 

 rise somewhat abruptly from the eastern plains to a height in places 

 of some C),000 or 7,000 feet. They are composed almost entirely of 

 Secondary and Tertiary sedimentary rocks, with occasional layers of 

 intrusive basalts, the whole tlirown up in a somewhat complicated 

 system of folds of usually monoclines or anticlines terminating 

 toward the west in a lofty escarpment, the crest of which overlooks 

 the deep, narrow, and irregular, eastern longitudinal valley that sep- 

 arates the eastern lateral range from the central main range of the 

 .\ndes. In this eastern longitudinal valley there is located a series 

 of the most beautiful mountain lakes, extending northward in a 

 somewhat broken chain from liake Argentina, at the head of the 

 Santa Cruz River, to the northern limits of Patagonia. At some dis- 

 tance to the south of Ijake Argentina the bottom of the valley has 

 not been suflicientl}^ elevated and it is here occupied, not b}' fresh- 

 water lakes, but by numerous narrow arms of the Pacific, as seen in 

 Last Hope Inlet, Obstruction Sound, Skj'ring and Otwa}' waters. and 

 Useless Bay, opi)osite Sandy Point, in the Strait of Magellan. 



