SUMMARY. 29 1 



ment, the crest of which overlooks the deep, narrow and irregular, eastern 

 longitudinal valley that separates the eastern lateral range from the central 

 main range of the Andes. In this eastern longitudinal valley there is 

 located a series of the most beautiful mountain lakes, extending north- 

 ward in a somewhat broken chain from Lake Argentino, at the head of 

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

 tance to the south of Lake Argentino the bottom of the valley has not 

 been sufficiently elevated and it is here occupied, not by fresh-water lakes, 

 but by numerous narrow arms of the Pacific, as seen in Last Hope Inlet, 

 Obstruction Sound, Skyring and Otway Waters, and Useless Bay, opposite 

 Sandy Point, in the Strait of Magellan. 



In many places important streams enter this great longitudinal valley 

 from the eastern plains and discharge their waters into the lakes, which in 

 turn are emptied into the Pacific through rivers intersecting the main 

 range of the Andes. This is true of all the lakes of this region, with the 

 one noted exception of Lake Argentino and its affluents. The upper 

 courses of the great transverse valleys of Patagonia are always directly 

 opposite some of the larger of these tributary valleys, so that at such 

 places the continental divide is exceedingly low and inconspicuous. This 

 condition, together with certain glacial phenomena, has led Dr. Moreno 

 to advance the theory that formerly all the lakes now found in the eastern 

 longitudinal valley discharged their waters into the Atlantic, and that their 

 diversion to the Pacific has been due to the damming of their eastern out- 

 lets with glacial drift. 



A careful examination of all the facts does not, I think, justify such an 

 assumption. I have examined with considerable care several of the low 

 continental divides about the eastern extremities of some of these lakes, 

 and have never found the original rocks there covered to any considerable 

 depth with glacial detritus. The great terminal moraines left by the former 

 ice-cap could always be seen crossing the transverse valleys some distance 

 to the eastward of the continental divide, where I have observed them to 

 have a thickness of more than 300 feet, as displayed in the bluffs of some 

 of the streams which have cut their way through these moraines in their 

 course to the Atlantic. 



A more plausible explanation, it appears to me, is afforded by a consid- 

 eration of the features at present existing throughout Patagonia and Tierra 

 del Fuego, in connection, with a proper understanding of the relative land 



