ORIGIN OF THE GLACIERS. 229 



The existence of great glaciers descending to the 

 sea-level on the west coast of South America, one of 

 which lies so far north as the Gulf of Penas, about 

 47° south latitude, is a necessary consequence of the 

 rapid depression of the line of perpetual snow on 

 the flanks of the Andes, as we follow the chain 

 southward from Central Chili to the channels of 

 Patagonia. The circumstance that permanent snow 

 is not found lower than about fourteen thousand feet 

 above the sea in latitude 34°, while only 8° farther 

 south the limit is about six thousand feet above the 

 sea-level, has been regarded as evidence of a great 

 difference of climate between the northern and 

 southern hemispheres, and more especially of excep- 

 tional conditions of temperature affecting this coast. 

 It appears to me that all the facts are fully explained 

 by the extraordinary increase of precipitation fi'om 

 the atmosphere, in the form of rain or snow, which 

 occurs within the zone where the rapid depression of 

 the snow-line is observed. So far as mean annual 

 temperature of the coast is concerned, the diminution 

 of heat in receding from the equator is less than the 

 normal amount, being not quite 5° Fahr. for 7° of 

 latitude between Valparaiso and Valdivia. But the 

 annual rainfall at Valdivia is eight times, and at 

 Ancud in Chiloe more than nine times, the amount 

 that falls at Santiago. Allowing that the dispropor- 

 tion may be less great between the snowfall on the 

 Cordillera in the respective latitudes of these places, 

 we cannot estimate the increased fall about latitude 

 40° at less than four times the amount falling ' in 

 Central Chili. When we further recollect that in the 



