ON THE OEIGIN OP MOUNTAIN BANGES. 



151 



crust, with a stratum of molten rock between. Mr. Osmond 

 Fishor advocates the latter view, Mr. Mellard Reade accepts 

 the former. All agree, however, that the interior of the 

 earth is intensely hot; all agree that this heat is being 

 gradually but slowly lost by radiation ; all agree tliat the 

 result of such loss of earth heat is tho contraction of the 

 earth's volume. But whereas the contractionists contend 

 that this earth-shrinkage is suiTicient in amount to produce 

 all those wrinkles on the face of mother earth which we 

 little mortals call mountain ranges, both Mr. Fisher and 

 Mr. Reade contest the sufficiency of this explanation. 



Sir William Thomson has established — that is, calculated 

 on tho assumed correctness of coi'tain data — tho law which 

 the tempoi'aturo within the earth must follow if it be a 

 solid cooling by conduction. Accepting this law, and mak- 

 ing use of tho results of experiment on the amount of 

 contraction tho rocks undergo on cooling, Mr. Fisher has 

 calculated the amount of inequalities of the earth's surface 

 which would have been formed had they been due to a hot 

 solid globe cooling by conduction, and finds that the amount 

 falls far slioi't of that which is found in tho inequalities 

 actually existent. For whereas the actual inequalities, if 

 levelled down, would form a layer of about 10,000 feet thick- 

 ness, those which would be formed on the present hypothesis 

 would form a layer certainly not exceeding 900 feet in 

 thickness, and probably not exceeding 200 feet in thickness. 

 (Fhysics of the UartVs Grust, p. 274.) 



Mr. Mellard Reade rejects the contraction hypothesis on 

 other grounds. He thinks " that an important link in the 

 chain of reasoning has been omitted, inasmuch as the shrink- 

 age of tho solid shell itself through tho gradual cooling of 

 its lower zones has been unconsidered in the application of 

 tho hypothesis." Ho draws attention to Mr. Fisher's calcu- 



