226 PATAGONIAN EXPEDITIONS: GEOGRAPHY. 



shingle up to within some five hundred feet of the top of the higher 

 tableland. 



While from the above facts it will become apparent, that the transverse 

 valleys and present drainage systems of Patagonia had their origin 

 before the last submergence of the land beneath the sea, it must not 

 be supposed that the present water courses agree in every instance with 

 those of the preceding period of erosion. In many instances these 

 ancient waterways have been so effectually clogged by sedimentary 

 materials or lava flows, that the present streams have been forced to find 

 for themselves new outlets, and in this they have, as is nature's custom, 

 followed along the lines of least resistance. Moreover, the recent elevation 

 throughout this region does not in all cases correspond accurately with 

 that of the last period of erosion, and this difference has, in some localities, 

 resulted in a considerable change in the position of the watersheds of 

 certain districts. Through this shifting of the watersheds and the damming 

 up of the courses of former drainage systems, aided very largely by the 

 present more arid climate of this region, there are to be found over its 

 surface many river channels long since abandoned and now completely 

 desiccated. The former courses of these old rivers may, as a rule, still 

 be very accurately traced by the chain of rather deep depressions that, 

 separated from one another by divides somewhat lower than the surface 

 of the adjoining pampas, still indicate the position and direction of the 

 former channel. 



Dr. Florentino Ameghino has held that the great transverse valleys of 

 Patagonia had their origin in gigantic faults. Like most of this writer's 

 observations on the geology and geography of Patagonia, this is given as 

 a dictujn to be taken solely on the authority of the author. This is the 

 more remarkable, since Dr. Ameghino has himself never seen any portion 

 of Patagonia. But, like his assertion that the Shingle formation was 

 deposited at the bottom of the sea without the aid of any intermediate 

 agency, as, for instance, that of ice, it was perhaps the best and only course 

 open to him. In both instances it illustrates the caution which should be 

 exercised before accepting the assertions or theories of men, however 

 learned, when they essay to speak authoritatively concerning questions, 

 with the facts bearing upon which they are absolutely unacquainted. As 

 regards the origin of the Shingle formation. Dr. Ameghino simply asserts 

 that it was deposited at the bottom of the sea and without the aid of any 



