SUMMARY. 293 



we have already remarked, had their origin previous to the last submer- 

 gence, would appear successively, first as straits connecting the two oceans, 

 and next as valleys, with deep bays along the coast. The Strait of Ma- 

 gellan is the last or most southerly of these great transverse valleys, and 

 still exists as a strait connecting the two oceans. 



Turning now to the eastern longitudinal valley, it will be seen that as 

 the elevation progressed it would at first be broken up into a series of 

 fiords and inlets toward the north, still communicating with the Pacific 

 through the deeper channels intersecting the main range of the Andes. 

 In time such communications would be severed and the heads and arms 

 of the fiords would be left as lakes to discharge their waters into the Pa- 

 cific by the last and deepest of the connecting channels. We have thus 

 represented between the Strait of Magellan and Lake Argentino every 

 stage in the development of the present lake systems of the southern Andes. 



A glance at one of Fitzroy's charts of the Magellan Strait instantly 

 reveals the fact that it is much deeper in the western than in the eastern 

 part. In fact, it is extremely shallow throughout its entire course from 

 Useless Bay eastward to Cape Virgin, and only a comparatively slight 

 elevation would here suffice to bring its bottom above sea-level and con- 

 vert it into a valley connecting Tierra del Fuego with the mainland, and 

 changing Useless Bay first into a fiord, and later into a lake as the eleva- 

 tion increased, sending its waters to the Pacific by way of the much deeper 

 western channels of the straits. 



The same conditions that exist to-day in the Strait of Magellan have 

 existed at some previous time over all the great transverse valleys of Pata- 

 gonia, and an elevation similar to that which has taken place more to the 

 northward would produce conditions along the course of this strait iden- 

 tical with those now existing farther north; So also an elevation of the 

 region south of Lake Argentino similar to that which has taken place north 

 of this lake would convert Last Hope Inlet, Obstruction Sound, Skyring 

 Water, and Otway Water from marine fiords connecting directly with the 

 Pacific into a series of fresh-water lakes discharging their waters into the 

 same ocean. 



At present Otway Water is separated from Cabeza del Mar, a small bay 

 extending inland from the eastern extension of the Magellan Strait, by a 

 narrow neck of land only eight miles in width, and with a maximum alti- 

 tude of perhaps less than 100 feet. Notwithstanding this low altitude, the 



