APPENDIX. 189 



development of force, such as the supposed generation of heat by chemical means, or such a 

 natural cause as the removal of materials from one part of the surface to another. The 

 theories I have to notice are more or less dependent upon one or other kind of cause. 



The cpiestion of mountain-formation seems but a special case of the general problem of the 

 inequalities of the solid surface of the globe. A first glance at 

 earth SymmetliCaI f ° rm ° f the these inequalities brings to notice their very unsymmetrical dis- 

 tribution. In connection with this fact Sir John Herschell 

 states in his Physical Geography (p. 15) that the centre of gravity of the earth is slightly 

 excentric to that of the external figure, and in the dhection from the hemisphere of greatest 

 elevation ; he further points out the necessary inference, that the force which sustains 

 our continents is one of tumefaction, such as would be produced by an increased 

 temperature beneath their area. Symmetry' being the necessary result of force acting 

 under homogeneous conditions, we have to seek the secondary or partial causes which 

 have resulted in the very unsymmetrical arrangement of the earth's surface as we now 

 find it. In such speculations we are of course limited to known causes ; for instance, it 

 would not be admissible in explanation of the earth's unsymmetrical form gratuitously to 

 suppose the presence of a larger volume of some peculiar light substance beneath the area of 

 most extensive elevation. The phenomenon in question is so extensive relatively to the whole 

 mass concerned that any cause which could by one operation produce such a result must 

 be considered general as regards our globe. We know of no such cause. We can conjecture 

 no agency by a single operation of which this unsymmetrical tumefaction of the earth's mass 

 can be produced. We are thus driven back to look upon the tumefaction as cumulative, and 

 upon its cause as local. In this way a case of general elevation seems to be brought back to 

 a special one. Even in those theories which introduce general causes for the production of 

 the special elevation of mountain chains the modifying influence of cumulative local causes 

 has to be recognized. For example, M. de Beaumont in the elaboration of his grand scheme 

 of ultimate symmetry allows that the actual tuberances (bossellements) of the surface cannot 

 be the simple result of any actual state of tension.* 

 In noting various theories of mountain-formation, I give precedence to that of M. de 



Beaumont, as detailed in his " Notice svr les systemes de monl- 

 De Beaumont's theory. ... ., . 



agnes ; it is beyond comparison the most elaborate in design and 



execution, and it treats the subject from the point of view of general cosmical action. It was 



observed that mountain chains are rectilineal - , or made up of rectilinear elements. By 



comparing these chains or elements of chains it was found that they cculd be arranged in 



groups, having a common direction, under certain conditions of parallelism. This result 



formed one premiseofM.de Beaumont's theory. The other was found as follows : — By 



examining the rocks composing, and contiguous to, a mountain chain, the relative date of the 



disturbance can be approximately ascertained ; mountains, and disturbances of every degree, 



* I have introduced this paragraph to place some limitation to the phrase so freely and so vaguely used by 

 geologists, and so likely to lead to misconception, namely, the expression continental eleoation. Very large areas 

 have no doubt undergone changes of level at one and the same time, but the formation of continents is probably 

 the result of very broken and disconnected chains of causation. In the present vague state of our knowledge 

 of the causes of elevation, and of our very limited acquaintance with facts, it is impossible to give an exact 

 meaning to the expression. The sense attached to it by the best authorities is, I think, as opposed to spasmodic, 

 lineal elevation. In its simple orographioal application there can be no ambiguity. 



