290 Sloping Terraces of Gravel paetii 



formed of red granite, mica- slate, and basalt, which all 

 have suffered a truly astonishing amount of denudation ; 

 the gravel in the valley, as well as on the talus-like 

 plain in front of it, is composed of these rocks ; but at 

 the mouth of the valley, in the middle (height proba- 

 bly about 3,500 feet above the sea), a few small isolated 

 hillocks of several varieties of porphyry project, round 

 which, on all sides, smooth and often white-washed 

 pebbles of these same porphyries, to the exclusion of 

 all others, extend to a circumscribed distance. Now, 

 it is difficult to conceive any other agency, except the 

 quiet and long-continued action of the sea on these 

 hillocks, which could have rounded and white-washed 

 the fragments of porphyry, and caused them to radiate 

 from such small and quite insignificant centres, in the 

 midst of that vast stream of stones which has descended 

 from the main Cordillera. 



Sloping Terraces of Gravel in the Valleys of the 

 Cordillera. — All the main valleys on both flanks of the 

 Chilian Cordillera have formerly had, or still have, their 

 bottoms filled up to a considerable thickness by a mass 

 of rudely stratified shingle. In central Chile, the 

 greater part of this mass has been removed by the 

 torrents ; cliff-bounded fringes, more or less continuous, 

 being left at corresponds g heights on both sides of 

 the valleys. These fringes, or as they may be called 

 terraces, have a smooth surface, and as the valleys rise, 

 they gently rise with them : hence they are easily irri- 

 gated, and afford great facilities for the construction of 

 the roads. From their uniformity, they give a re- 

 markable character to the scenery of these grand, wild, 

 broken valleys. In width, the fringes vary much, 

 sometimes being only broad enough for the roads, and 

 sometimes expanding into narrow plains. Their sur- 

 faces, besides gently rising up the valley, are slightly 



