150 



ON THE ORIGIN OP MOUNTAIN EANGES. 



in the eyes of geologists, is that according to which moun- 

 tain ranges are regarded as the wrinkles on the earth's 

 stirfaco due to contraction consequent upon the fall of tem- 

 perature which I'csults from the constant radiation of earth- 

 heat into space. Many facts of mountain structure, the 

 extreme plication of the strata, the fan-structure, and the 

 linear compression; and many facts of mountain distribu- 

 tion, the subsidiary spurs which accompany groat ranges, and 

 the complementary arrangement of the Eurasian systems, 

 east and west, and the American, north and south, have 

 been held to be readily explicable on this hypothesis. 



But in 1881 the publication of the Physics of the Earth's 

 Crust by Mr. Osmond Fisher, once a firm supporter of con- 

 traction, but herein an advocate of other views, dealt it a 

 heavy blow, all the weightier from its (to most geologists) 

 incomprehensible mathematics. Captain Button and other 

 American geologists, well acquainted with all the details of 

 mountain stracturo in the great western continent, have 

 weighed it in the balance and pronounced it wanting. In 

 the antipodes Captain Hutton is an old opponent with a 

 rival theory of his own. And now Mr. Mellard Ileado enters 

 the field and contends that, not to contraction, but to ex- 

 pansion within the crust of the earth, are we to attribute 

 the birth of a mountain range. 



In any consideration of mountain-building a preliminary 

 problem has to bo dealt with. What is the condition of the 

 interior of the earth ? The old view of a molten globe 

 surrounded by a thin solid crust is now held only by the 

 few who are content to ignore, or who dare dispute, the re- 

 sults of physical and mathematical investigation. Geologists 

 must choose between the two views which, we are confi- 

 dently told, are alone physically possible : that of complete 

 and thorough solidity, and that of a solid core and solid 



