262 



CHARLES DARWIN 



alleled in other parts of the world, not far from the latitude 

 of Concepcion, where the land ceases to be covered with for- 

 est-trees; for trees in South America indicate a rainy cli- 

 mate, and rain a clouded sky and little heat in summer. 



The descent of glaciers to the sea must, I conceive, mainly 

 depend (subject, of course, to a proper supply of snow in the 

 upper region) on the lowness of the line of perpetual snow 

 on steep mountains near the coast. As the snow-line is so 

 low in Tierra del Fuego, we might have expected that many 

 of the glaciers would have reached the sea. Nevertheless, 

 I was astonished when I first saw a range, only from 3000 to 

 4000 feet in height, in the latitude of Cumberland, with every 

 valley filled with streams of ice descending to the sea-coast. 

 Almost every arm of the sea, which penetrates to the interior 

 higher chain, not only in Tierra del Fuego, hut on the coast 

 for 650 miles northwards, is terminated by " tremendous and 

 astonishing glaciers," as described by one Qf the officers on 

 the survey. Great masses of ice frequently fall from these 

 icy cliffs, and the. crash reverberates like the broadside of a 

 man-of-war through the lonely channels. These falls, as 

 noticed in the last chapter, produce great waves which break 

 on the adjoining coasts. It is known that earthquakes fre- 

 quently cause masses of earth to fall from sea-cliffs: how 

 terrific, then, would be the effect of a severe shock (and such 

 occur here") on a body like a glacier, already in motion, and 

 traversed by fissures ! I can readily believe that the water 

 would be fairly beaten back out of the deepest channel, and 

 then, returning with an overwhelming force, would whirl 

 about huge masses of rock like so much chaff. In Eyre's 

 Sound, in the latitude of Paris, there are immense glaciers, 

 and yet the loftiest neighbouring mountain is only 6200 feet 

 high. In this Sound, about fifty icebergs were seen at one 

 time floating outwards, and one of them must have been at 

 least 168 feet in total height. Some of the icebergs were 

 loaded with blocks of no inconsiderable size, of granite and 

 other rocks, different from the clay-slate of the surrounding 

 mountains. The glacier furthest from the pole, surveyed 

 during the voyages of the Adventure and Beagle, is in lat. 



*S Bulkeley's and Cummin's Faithful Narrative of the Loss of the Wager. 

 The earthquake happened August 25, 1741. 



