2o6 Valley of Santa Cruz. paet n. 



plain was generally wider than the lower ones — as 

 indeed follows from the valley from A (n) to A (s) 

 being generally nearly double the width from B (?z) 

 to B (V). Low down the valley, the summit-plain A (s) 

 is continuous with the 840 feet plain on the coast, but it 

 is soon lost or unites with the escarpment of B (s). 

 The corresponding plain A (ti). on the north side of the 

 valley, appears to range continuously from the Cordil- 

 lera to the head of the present estuary of the S. Cruz, 

 where it trends northward towards Port St. Julian. 

 Near the Cordillera the summit-plain on both sides of 

 the valley is between 3,200 and 3,300 feet in height; 

 at 100 miles from the Atlantic, it is 1,416 feet, and on 

 the coast 8-40 feet, all above the sea-beach ; so that in 

 a distance of 100 miles the plain rises 576 feet, and 

 much more rapidly near to the Cordillera. The lower 

 terraces B and C also appear to rise as they run up the 

 valley ; thus D (n), measured at two points twenty- 

 four miles apart, was found to have risen 185 feet. 

 From several reasons I suspect, that this gradual 

 inclination of the plains up the valley, has been chiefly 

 caused by the elevation of the continent in mass, 

 having been the greater the nearer to the Cordillera. 



All the terraces are capped with well-rounded gravel, 

 which rests either on the denuded and sometimes 

 furrowed surface of the soft tertiary deposits, or on the 

 basaltic lava. The difference in height between some 

 of the lower steps or terraces seems to be entirely 

 owing to a difference in the thickness of the capping 

 gravel. Furrows and inequalities in the gravel, where 

 such occur, are rilled up and smoothed over with sandy 

 earth. The pebbles, especially on the higher plains, 

 are often whitewashed, and even cemented together by 

 a white aluminous substance ; and I occasionally found 

 this to be the case with the gravel on the terrace D. 



