222 PATAGONIAN EXPEDITIONS'. GEOGRAPHY. 



sea. I may also add that these same beds have been observed at various 

 other localities, throughout the slopes of the Andes, along the coast, and 

 at intermediate points, and that it has been practically demonstrated that, 

 where they have not been removed by erosion, their distribution is coex- 

 tensive with that of the Shingle Formation. The present distribution of 

 these marine deposits, which I have called the Cape Fairweather beds, 

 and which are filled with the shells of brachiopods, oysters, trophons, and 

 other marine invertebrates, is positive proof that, at a time even as recent 

 as late Pliocene, this entire region was submerged beneath a shallow sea. 

 Moreover, the great thickness of the Cape Fairweather and underlying 

 Santa Cruzian and Patagonian beds, taken in connection with their high 

 inclination along the slopes of the Andes, dempnstrates that, although 

 some former period may have witnessed the birth of these mountains, and 

 that while they may have been represented by a chain of islands in the 

 midst of this Pliocene sea, it was the close of the latter period that wit- 

 nessed those great orographic movements, which were so stupendous as 

 to transform this chain of islands, if indeed such really did exist, into lofty 

 mountain ranges. This upthrust, at first central and most pronounced 

 along the present axis of the Andean region, was gradually extended east- 

 ward, so that when what are now the eastern plains commenced to appear 

 above the level of the sea, the Andes had already reached an elevation 

 sufficient to cause the accumulation over their summits of vast fields of 

 snow and ice. These, in turn, gave rise to glaciers, which moved down 

 the slopes of the mountains and spread out over the adjacent plains or 

 passed into the deep valleys, which had been cut in the latter at a time 

 previous to their last submergence, and many of which were still occupied 

 by arms of the sea. The snow and ice of such glaciers, during their long 

 journey from the summits of the mountains, would become heavily charged 

 with debris, derived from the slopes of the latter. This would later be 

 left as moraines at the face of the glacier, or where such glaciers terminated 

 in an arm of the sea, be thrown to the bottom by the melting ice, or, if 

 the waters were of sufficient depth for the formation of icebergs, then 

 much of the material would be more widely distributed, the distribution 

 depending on the size of the bergs and the direction of the currents or 

 winds. The presence of terminal moraines, which, as has been mentioned 

 in the Narrative, occur at frequent intervals throughout these plains, at dis- 

 tances of even fifty miles or more from the foothills of the Andes, is suffi- 



