THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE V. VOL. X. 



No. IX.— SEPTEMBER, 1913. 



OTiXG-Xl^J^JL. .A.I?.TIOI-.E3S. 



I. — The Oeigin of Mountains. 

 By Colonel S. G. BUKRARD, C.S.I.,E.E., F.E.S., Surveyor-General of India. 



1. The reply by the Rev. 0. Fisher (Geological Magazine, June, 

 1913, p. 250) to Sir Thomas Holland's note leads me to ask permission 

 to place the geodetic case before your geological readers. I ask 

 geologists to give a hearing to a geodetic computer. 



No living man has done more to encourage geodesists and to create 

 a geological interest in their work than Osmond Fisher ; no man has 

 done so much to impress upon geologists that they cannot afford to 

 ignore geodetic results as he has; no other man has had the advantage 

 of being able to speak with authority both as a mathematician and as 

 a geologist. We recognize the weight of his opinion. May I explain 

 why we have the presumption to differ from some of his conclusions ? 



2. Mr. Fisher has explained the origin of mountain ranges by what 

 is known as the ' floating crust hypothesis ', in which he assumes 

 a solid crust floating upon a liquid substratum. He accepts the 

 principle of isostasy in its entirety, and holds that mountain ranges 

 are supported, not by the rigidity of the earth, but by floatation like 

 icebergs. 



Geodetic computers find three objections to Mr. Fisher's hypothesis : 

 Firstly, we think that no hypothesis can be accepted now that 

 is dependent upon the assumption of a liquid interior to the earth, 

 and in this point we are in agreement with Sir Thomas Holland. 

 Secondly, Fisher's hypothesis is not generally applicable to all 

 continents and to all mountains, but has to be ' amplified ' or 

 ' modified ' when any particular topographical feature comes under 

 analysis. Thirdly, Fisher assumes that the depth of compensation 

 of a mountain is directly proportional to its height above sea-level ; 

 this assumption is opposed to the results of geodetic observations. 



3. Mr. Fisher has argued that the rotation of the earth will give 

 to the liquid interior an effective rigidity; but this rotation has 

 conferred no rigidity upon our oceans, and even if it did render the 

 liquid interior rigid, it would only do so in low latitudes where 

 the rotation velocity is high. I understand, moreover, that the earth's 

 interior was assumed by Mr. Fisher to be liquid, in order to explain 

 the floatation of the crust. If the liquid is now proved to be rigid, 

 the crust cannot be floating upon it. 



4. I said above that Mr. Fisher's theory is not generally applicable : 

 may I explain what I mean? If he would define his theory in 



DECADE V. — VOL. X. — NO. IX. 25 



