230 PATAGONIAN EXPEDITIONS : GEOGRAPHY. 



having even the slightest personal knowledge of Patagonia could have 

 asserted that "such deposits do not exist." 



In the preceding paragraphs dealing with the origin and age of the 

 transverse valleys of Patagonia, I think it has been very clearly shown 

 that they are all true valleys of erosion and that they had their origin in 

 that period of erosion which immediately preceded the last submergence 

 of that country, which latter period witnessed the deposition of the Cape 

 Fairweather beds. The comparatively thin layer of marine deposits with 

 which the Santa Cruzian beds were covered, was, for the most part, 

 removed by erosion during the slow emergence of this region from the 

 sea. Only in especially favored localities could so thin a covering of such 

 soft materials successfully resist the powerful erosive action of the tides 

 of this coast. Thus it is that we only find remnants of this formation at 

 infrequent intervals along the coast and throughout the interior, where it 

 is now generally covered over by the Shingle formation, not vice versa, as 

 Ameghino, with his usual propensity for reversing the sequence of geolog- 

 ical formations, has stated. The formation of the beds of bowlders or 

 shingle, as has already been shown, commenced when this period of ele- 

 vation set in, has continued as it progressed, and is still going on. 



For a long time after the adjoining plains were brought above the level 

 of the sea, these valleys remained submerged and appeared first as narrow 

 straits connecting the waters of the two oceans. Later, as the elevation 

 proceeded, such waterways were broken up and there appeared at their 

 eastern and western extremities long and narrow inlets from the respective 

 oceans. The Straits of Magellan are, in reality, the southernmost of these 

 great transverse valleys and still exist as a strait, though at present a 

 relatively very slight elevation would suffice to break the continuity of 

 their waters and unite Tierra del Fuego with the mainland. As I shall show 

 later, this continuance of the Magellan valley as a strait long after the 

 valleys to the north had been elevated above the sea, is a natural con- 

 sequence of the point of origin and direction of the orographic movement, 

 which has resulted in the present elevation of the region under con- 

 sideration. I shall show that this elevation began in the north and 

 has gradually extended to the southward and eastward, that its maxi- 

 mum force has been exerted along a line essentially concident with the 

 present axis of the southern Andean Mountain System and that it is 

 still in progress. 



