388 



PASSAGE OF CORDILLERA. March, 1835. 



The features in the scenery of the Andes which struck me 

 most, as contrasted with the few other mountain chains with 

 which I am acquainted, were, — the flat fringes sometimes 

 expanding into narrow plains on each side the valleys, — the 

 bright colours, chiefly red and purple, of the utterly bare 

 and precipitous hills, — the grand and continuous wall-like 

 dikes, — the strongly-marked strata which, when nearly ver- 

 tical, form the most picturesque and wild pinnacles, but 

 where less inclined, great massive mountains ; the latter 

 occupying the outskirts of the range, and the former the 

 more lofty and central parts, — lastly, the smooth conical 

 piles of fine and brightly-coloured detritus, which slope at 

 a high angle from the flanks of the mountains to their bases, 

 some of the piles having a height of more than two thou- 

 sand feet. 



I frequently observed both in Tierra del Fuego', and 

 within the Andes, that where the rock was covered during 

 the greater part of the year with snow, it was shivered in 

 a very extraordinary manner into small angular fragments. 

 Scoresby* has observed the same fact in Spitzbergen: he 

 says, The invariably broken state of the rocks appeared to * 

 have been the eff*ect of frost. On calcareous rocks, some 

 of which are not impervious to moisture, the eff'ect is such 

 as might have been expected ; but how frost can operate in 

 this way on quartz is not so easily understood.^' The whole 

 phenomenon appears to me rather obscure : for that part of 

 the mountain which is covered during many months by a 

 mantle of snow, must be less subject to repeated and great 

 changes of temperature than any other, yet it is the most 

 affected. I have sometimes thought, that the earth and 

 fragments of stone lying on the surface, were perhaps less 

 effectually removed by means of slowly percolating snow- 

 water,t than by the agency of rain, and therefore that the 



* Scoresby's Arctic Regions, vol. i., p. 122. 



f I have heard it remarked in Shropshire, that the water, when the 

 Severn is flooded from long-continued rain, is much more turbid, than 

 when it proceeds from the snow melting on the Welsh mountains. The 



