Considerations connected with the Glacier Theory • 41 



viously have taken place, or at least the hardened outer crust 

 could no longer follow completely the contraction of internal 

 nucleus. But, as according to Fox, granite, from its red-hot 

 condition down to the usual temperature, contracts by about 

 0.02, this would, in the case of Mont Blanc, amount to 300 

 feet for the portion projecting above the level of the sea, 

 without taking into consideration that greater elevation of 

 temperature and expansion of the portion of the vast crust 

 of the earth on which the Alps rest, which must necessarily 

 have been combined with this eruption, and which must, in a 

 great measure, have existed after the cooling of the mountain?, 

 and without including the expansion of the merely elevated 

 Neptunian strata. That, further, the sinking of a newly 

 formed range of mountains, produced by the agency of fire, 

 can be still measured within a short period, when that range 

 is susceptible of being covered externally with snow, is proved 

 by Boussingault's report on the Andes, in which chain the 

 mountain of Quaguapichincha, near Quito, though now clear 

 of snow on its summit, was covered with so much a hundred 

 years ago that the French geometricians were interrupted in 

 their labours ; the volcano of Purace also, near Popayan, ac- 

 cording to the assertion of the inhabitants, has its snow line 

 nearer the summit than formerly ; and, according to the 

 measurements of Boussingault, Quito, Popayan, Santa Fe de 

 Bogota, and the Meierei of Antisana, are not so high now as 

 they were found to be thirty years ago by Caldas and Hum- 

 boldt. These portions of the Andes consist of trachytic rocks, 

 which contract only by 18 instead of 25 per cent. We are, 

 therefore, rather entitled to say, that nothing favours the sup- 

 position that the Alps have constantly possessed the same 

 height above the level of the sea since their elevation. 



Nevertheless, it is not my intention to deny all diminution 

 of the temperature of the earth's surface, or even local altera- 

 tions of temperature since the disappearance of the elephants. 

 As, however, it was only in the last period of the earth that 

 the temperate zone could be more and more distinguished 

 from the hot, and the cold from the temperate, a degree of 

 medium temperature was thus so unequally distributed over 

 the surface of the earth, that such a temperature would not be 



