THE PYRENEES. 25 



of course varies in different localities, as well as with 

 the seasons of the year. It is uniformly higher on 

 the southern or Italian face of the Alps than on the 

 northern or Swiss side, and it naturally descends 

 lower during the winter than during the summer 

 season, but at a greater height than 9000 feet the 

 snow" never melts.* The accumulating mass which 

 successive winters form in the elevated regions is 

 impelled downward by its gravity into the lower 

 valleys, where it forms the well-known glaciers." 



To quit the Alps and speak of other mountain 

 ranges, I am reminded that the passes through the 

 Balkans, though of no great altitude, consist of deep 

 and narrow defiles, yet none of these mountains reach 

 the height of perpetual snow. 



The roads across the Pyrenees consist of deep 

 and narrow defiles, with high walls of rock on either 

 hand. The southern face of the Pyrenees is more 

 rugged and precipitous than its northern slope, so 

 that the ascent on the side of Spain is generally 

 more difficult and laborious than from the French 

 side of the mountain. 



The inclination of the northern declivity of the 

 Pyrenees is from 3° to 8" ; that of the southern de- 

 clivity of the highest Alpine mountains is only yA°. 

 Notwithstanding this circumstance, it is necessary to 

 mount at times much steeper inclinations. Even a 

 slope of between 7° and 8° is very considerable ; in 

 fact, it is almost the maximum for vehicles. In 

 France the regulations are that the road shall never 

 exceed an inclination of 4° 46". An inclination of 15° 

 can hardly be overcome by animals encumbered with 



* In central Europe. In warmer regions, and those nearer the 

 equator, the snow-line is of course at a greater altitude. 



