352 J. B. Hatcher — Geology of Southern Patagonia. 



basalt ; these also must have extended in a comparatively uni- 

 form manner, without forming the steep cliffs which they 

 exhibit to-day in the river valleys. Darwin, speaking of the 

 scarps of the valley of the river Santa Cruz, said that the cliffs 

 of basalt of the two opposite sides were recognizable imme- 

 diately as at one time forming a continuous bed. The same 

 may be said of the beds of bowlders which in many parts form 

 the opposite cliffs of the Patagonian valleys ; those beds were 

 continuous across the valleys, but there are now no traces of 

 them. 



" It is evident that if the valleys had existed before the 

 great marine submergence referred to, they would have been 

 completely filled with marine deposits, which, even supposing 

 they had been swept away afterwards by the waters, would 

 always have left numerous traces buried in the innumerable 

 angles of the slopes ; but as such deposits do not exist, the 

 inevitable conclusion is, that the formation of the great trans- 

 verse valleys of Patagonia was brought about by great disloca- 

 tions and gigantic faults at a comparatively recent geological 

 period, posterior to the bowlder formation and at the last 

 emergence of the land." 



If, as Dr. Ameghino states, " it is evident that at the bottom 

 of the ancient sea in which the bowlders were deposited these 

 were scattered by the waters in a uniform manner over all the 

 submerged territory," is it consequently evident, as he con- 

 cludes, that "if the valleys had existed before the great marine 

 submergence referred to, they would have been completely 

 filled with marine deposits," when these valleys are all many 

 times deeper than the entire thickness of the bowlder formi- 

 tion ? It certainly is not evident that these valleys would have 

 been completely filled with marine deposits ; but it is quite 

 evident, that over their slopes and in their bottoms there 

 would have been deposited a layer of bowlders, at least equal- 

 ling in thickness that of the bowlder beds of the table lands. 

 It is further evident, that supposing they had been afterwards 

 swept away by the waters, they would have left numerous 

 deposits buried in the innumerable angles of the slopes ; and 

 this is just what is to be seen in the sides of the canons and 

 larger water courses at almost every section shown along the 

 coast or elsewhere. In fig. 6 are shown not only the bowlder 

 formation but also the underlying Caps Fairweather beds, both 

 occupying angles in the slope. In figs. 10 and 11 the remnants 

 of the bowlder formation are shown occupying angles in the 

 slopes of the canons along this coast. At the points where 

 both the latter sections are shown, it is quite possible to deter- 

 mine the relative amount of erosion which has taken place 

 prior to and since the deposition of the bowlder formation. 



