GEOLOGY. 



639 



In Europe, the mantle of eternal snow, which buries in 

 death all the upper regions of our mountains, generally be- 

 gins at a height of 8900 to 9200 feet. In equatorial Amer- 

 ica the limit of these incessant frosts is almost half as high 

 again, while at Spitzbergen it sinks to the level of the sea 

 (see Fig. 238). 



This imposing shroud of snow, by its calm majesty, some- 

 times gives an air of fantastic lightness to the loftiest peaks. 

 When these are softly undulated, they are often taken at a 

 great distance for a transparent curtain of motionless clouds 



2J9. Mount Erebus, Antarctic Regions. 



scattered upon the horizon. The chain of the Alps often 

 appears like this. The eye is frequently deceived, espe- 

 cially towards evening, and the conviction that they are 

 really mountains is only acquired by observing that the 

 false clouds do not undergo the least change of form, whilst 

 if they were true ones a few minutes would suffice to 

 change their outline. 



Sometimes, also, the diadem of snow which crowns a 

 mountain becomes the theatre of the most unusual phenom- 



