86 PROCEEDINGS Of THE GEOLOGICAL SOCIETY. [DeC. 17, 



in similar positions might be much the same ; but the greater extent 

 of land which must have existed in the northern hemisphere, as 

 compared with the southern, in the more recent geological periods, 

 must have rendered the summer temperature greater in the northern 

 than in the southern hemisphere, and consequently the snow-line 

 and, ccBteris paribus, the lower extremities of the glaciers somewhat 

 higher in the former than the latter region. The great distinction, 

 however, between the western coast of South America and that of 

 Europe consists in the great diiference in the heights of their moun- 

 tains. A glacier is described by Mr. Darwin* as descending to the 

 sea-level in the Gulf of Penas, on the west coast of South America, 

 in latitude 46° 40'. According to Dove's map, we have for that 

 place — o 



July temperature 40 F. 



January temperature .... 50 



Mean annual temperature 45 



Hence the height of the line of 32° must be about 4500 feet. The 

 diiference between the January and July temperatures is only 10°, 

 the latter being considerably reduced by the cold current passing 

 round Cape Horn. This, with the proximity of the Pacific, is highly 

 favourable to a low position of the snow-line. It may probably lie 

 n<^ar the line of 32°, or even considerably lower, in which case the 

 glacier must descend between 4000 and 5000 feet below it. This 

 coincides with the distances to which almost all glaciers of the first 

 order descend below the snow-line (art. 23, p. 81) and presents no- 

 thing anomalous. It is described as a very large glacier, descending 

 from a lofty mountain, which rises, undoubtedly, many thousand feet 

 above the snow-line. It is in this respect that the analogy between 

 the glaciers of South America and those which may have formerly 

 existed on such mountains as those of the British Islands entirely 

 fails. With the same climatal conditions, we might have glaciers 

 descending to the sea-level in the one case, without a trace of glaciers 

 in the other. 



29. I shall now discuss the case of the Alps. Adopting the hy- 

 pothesis of a current from the north, it is manifest that sucJh a current 

 would, as already remarked, tend much to equalize the temperature 

 from the latitude of Snowdon to that of the Alps in the present 

 region of western Europe, precisely as the Gulf-stream now equalizes 

 in so remarkable a degree the temperatures of different latitudes in a 

 considerable portion of its course in the northern ocean. If we 

 assume its effect on the mean annual temperature of the Alpine 

 region to be 8° or 9°, instead of 3° or 4°, as in the Snowdonian 

 region, we shall probably not over-estimate its influence. The mean 

 annual temperature would be thus reduced to about 45°. The height 

 of the line of 32° would then be about 5000 feet. The difference of 

 summer and winter temperatures would be considerably less than at 

 present, and the position would approximate much nearer to the 

 character of an insular one. Both these circumstances would be 



* Darwin's Journal, p. 284. 



