SUBTERRANEAN CHEMICAL FORCES. 403 



extinct since the elevation of the rocky and 

 Alleghany mountains above the ancient sea that 

 once covered the northern hemisphere : while in 

 South America, and on the eastern continent, 

 volcanos are numerous, but confined chiefly to 

 the borders of the ocean. The only feeble re- 

 mains of subterranean chemical action in North 

 America are its warm springs, which convey off 

 whatever heat is generated below the surface, in 

 a tranquil manner. 



The same observations apply to the greater 

 part of Europe and Asia, The Alps, the Appe- 

 nines, the Himalayas, and many other moun- 

 tain ranges of the old world, afford no evidence 

 of existing subterranean combustion, except the 

 numerous warm springs that issue from their 

 sides. Were it not for this continual discharge 

 of heat, it is probable that they might still be 

 convulsed at long intervals by volcanic explo- 

 sions, or by earthquakes, which are owing to 

 the confinement of volcanic steam by superin- 

 cumbent pressure. Warm springs may there- 

 fore be regarded as " safety valves of the globe," 

 still more emphatically than volcanos. It is very 

 well known that when the great Geyser of Ice- 

 land is obstructed by throwing stones into its 

 funnel, its temperature rises rapidly, which is 

 soon followed by eruptions of steam and water 

 to a great height. It is equally certain, that if 

 the obstruction were equal to the pressure of 



