places the surface of this will support a pedes- 

 trian, but commonly it is too weak for this; and, 

 as John Muir says, in getting through, over, 

 under, or across growths of this kind, one loses 

 all of his temper and most of his clothing! 



Timber-line is largely determined by cli- 

 matic limitations, by temperature and mois- 

 ture. In the Rocky Mountains the dry winds 

 are more deadly, and therefore more deter- 

 mining, than the high winds. During droughty 

 winters these dry winds absorb the vital juices 

 of hundreds of timber-line trees, whose withered 

 standing skeletons frequently testify to the 

 widespread depredations of this dry blight. A 

 permanent advance, too, is made from time to 

 time. Here and there is a grove, a permanent 

 settlement ahead of and above the main ranks. 

 In advance of these are a few lone trees, heroes 

 scouting in the lead. In moist, sheltered places 

 are seedlings and promising young trees grow- 

 ing up in front of the battle-scarred old guard. 

 Advances on dry, wind-swept ridges are more 

 difficult and much less frequent; on a few dry 

 ridges these trees have met with a repulse and 



58 



