MOUNTAINS; MINING; FORESTRY 205 



Fissures extending to great depth were made when the rigid 

 rock beds were folded, and erosion has made sharp peaks and 

 narrow clefts. Such mountains are called young mountains, 

 as if there had not been time enough for the work of the 

 atmosphere to smooth the rough places, round the sharp 

 points, and carry rock fragments down the sides into valleys 

 where they might be borne away by the streams. Some- 

 times young mountains are older in years than others which 

 appear older, because hardness of the rock or an arid climate 

 has delayed the work of change, and their features are still 

 rugged. 



228. Degradation. The process of lowering the land 

 has been occurring ever since there was any land above the 

 level of the sea. The work of the atmosphere tends to sepa- 

 rate and loosen particles at the surface of the rock; wind and 

 rain carry them away. The result of this work is denudation 

 or uncovering. A new surface is then exposed, and the 

 work continues, all the time lowering the average level of 

 the land. But while degradation is taking place, the land 

 is also being raised slowly by the wrinkling of the solid 

 crust of the earth, so. that the land has not yet been brought 

 down to the level of the ocean. The Appalachian Moun- 

 tains have been degraded from an original height equal to 

 that of the Rocky Mountains. The Adirondacks and White 

 Mountains are much degraded and southern New England 

 is worn down almost to a plain. 



229. Veins. The folding of the rocks of the earth, the 

 breaking which accompanies folding, and the erosion which 

 follows, have been the means of bringing valuable minerals 

 near the surface on mountain sides. Here they can be more 

 easily mined than if they lay far below a level surface. In 

 the process of formation, the fissures in the rocks were 

 filled with minerals in solution or in a state of vapor. 

 Crystals were deposited from these solutions on the sides 

 of the fissures, sometimes completely filling them. Such 



