GORGES AND RAVINES. 169 



found to run through its mountains-gaps or 

 passes." 



The gorges that have been mentioned seem princi- 

 pally due to faults and shrinkage fissures, but there 

 are others that appear to be nearly solely due to the 

 weathering out of courses or dykes of rock. Those 

 due to soft or " rotten " courses of rock often occur 

 in granite countries, where narrow, deep passes, with 

 steep or overhanging walls, often cut through a hill 

 or mountain range. Why these narrow, rotten courses 

 should occur in granite has not as yet been explained ; 

 but they weather much more quickly than the mass 

 of the rock; this being probably due not only to a 

 different chemical composition, but also to their 

 being intersected with innumerable small, irregular 

 shrinkage fissures or cracks, through which frost, 

 heat, rain, and wind easily penetrate into the rock, dis- 

 integrating it, and carrying away the particles, there- 

 by quickly forming more or less deep, narrow ravines. 

 Small ravines of this class are not uncommon in 

 our granite-hills, but they are seldom as well 

 developed or as striking as those of some other 

 countries. Mr John Muir, when describing the 

 newly-discovered " living glaciers " in California, 

 mentions the " narrow-slotted canons, called devil's 

 lanes, devil's gateway," &c., which are often from 

 100 to 200 or more feet deep, while they may be only 

 10 or 15 feet wide. Many of these gorges he finds 



