HuttOn. — On the FornuiUon of Mountains. 289 



11 "9 yards in 2,000 yeai"S, the time during which we have astronomical obser- 

 vations, or 1 inch in 4| years. 



9. If, however, for the sake of argument, we allow Mr. Fisher all he asks, 

 namely, that a mountain half a mile high might be formed on every 100 miles 

 since the present surface features originated, we then find that, taking the 

 date as before, Mr. Fisher's mountain has taken 11 millions of yeai-s to rise 

 2,640 feet, or it has risen only 1 foot in 4,166 years, which is slower than the 

 ascertained rate of denudation. 



Mr. Fisher, therefore, is in this dilemma : either the contraction of the 

 earth's radius has been so rapid that astronomers ought to have detected it ; 

 or else elevation has been so slow that no land could rise above the sea level. 



10. Another important objection to the contraction theory, is that 

 mountains have always been formed in those places whei'e deposits have been 

 heaviest ; while, by that theory, those ai-eas should never rise at all. Mr. 

 Fisher says that " the local pressure caused by a fresh deposit * * will 

 originate a line of elevation along its shore line or boundary," and again, " the 

 thickness of the rigid crust being increased by the new deposit, it would offer 

 an impediment to the elevation of ridges beneath it, and throw the whole 

 disturbance into the region just outside its boundary." This is exactly 

 opposite to what we see in nature. 



11. In my previous papers on this subject I have pointed out that 

 mountains are formed on two different plans, the one being associated with 

 volcanic rocks, the other with the crystalline schists ; but the contraction 

 theory supposes that all mountain chains are identically formed. 



12. My last objection is, that this theory makes no provision for tension 

 in rocks — everything is done by compression ; while faults prove tension ji;st 

 as surely as contortions prove compression. 



I am therefore of opinion that the effect on the crust caused by contraction 

 has been very small, and that it has been totally obliterated by the much 

 larger effects caused by deposition. 



In conclusion, I wish to explain that I do not consider it necessary that 

 the whole of an area must have been under water in order that it may be 

 raised by the deposition of limestone ; but that, owing to the lateral conduction 

 of heat, one or more mountain ranges might project ovit of it as islands. Indeed, 

 I believe that all high mountain ranges_are the result of several subsidences 

 and elevations, during which they may never have totally disappeared imder 

 the ocean. 



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