APPENDIX. 203 



(granitic) rocks, because in the former case a complete rupture to the surface took place 

 in the incipient stage of mountain formation, while in the latter, which he calls one of 

 subterranean volcanic action, the successive elevatory impulses were satisfied by intrusions 

 below the surface. 



In speculating upon the actual conditions of these phenomena Mr. Darwin gives strong- 

 evidence,— such as the co-instantaneous ejection of lava from distant orifices, and the rapid eleva- 

 tion of extensive areas, — for the supposition that the interior of the earth is in a molten condi- 

 tion. But he rejects as inadequate any hypothesis that has been formed of the prime mover in 

 these operations, concluding " that the configuration of the fluid surface of the earth's nucleus 

 is subject to some change, its cause completely unknown, its action slow and intermittent, but 

 irresistible. 



The great dissimilarity of structure exhibited in the foregoing examples of mountains, even 



making liberal allowance for incorrect observations, will suffice to 

 Great dissimilarity of struc- 

 ture, show how comprehensive a complete theory of mountain formation 



must be, and how very various the primary and secondary causes 



must be to produce results so unlike. It is obvious that in many cases it may be necessary to 



look beyond the actual mountain tract to obtain complete evidence of the original phenomena 



of disturbance. In commenting on the Appalachian section I gave an illustration of this : I 



showed the possibility of those mountains being but a remnant of a greater range long since 



obliterated. Mr. Rogers' sections suggest such an idea. Mr. Hall, however, makes these 



mountains independent, and, as it were, self-created. 



The dissimilarity in the structure of mountain ranges might have been made much more 



striking. We have been taking a somewhat one-sided view 

 True mountains. 



only, attending to such cases as are the result of the fracture and 



contortion of strata, but there are very large and considerably elevated areas, constantly 

 spoken of as mountain ranges, to which we must attach a different interest to that given to 

 what some geologists call true mountains, such as those we have been considering. There 

 are, for instance, the Western Ghats of Hindustan, more lofty and precipitous than the 

 Alleghanies, but they are for the most part made up of undisturbed strata, and offer little 

 or no illustration of the special question under discussion. The difference between the so 

 called true and other mountains is only one of degree. The object of interest is more or 

 less common to all, namely, the internal condition of the earth and the manner in which 

 it affects the crust ; thus every elevated area may be said to involve the supposition of a 

 crust movement, and may in some manner be a record of it, but it is only through the Assur- 

 ing and disturbance of strata that we can obtain any satisfactory information as to the 

 amount and direction of these crust movements, and hence the special importance of true 

 mountains. It is the necessary tendency of every elevatory action to produce Assuring, and to 

 result in distortion, but under certain conditions, such as those conceived by M. de Beaumont, 

 in which the whole earth is supposed to take part, or even by a less general cause, very exten- 

 sive elevation may occur without any such result. All Assuring and tilting of strata belong 

 to the same special branch of study as true mountains, which study has for its object the 

 fixation of the extent, amount, form, and duration of the disturbances of the earth's crust. 



If we endeavour to extract the elements of observation from the foregoing theories, it is dis- 

 appointing how little we obtain. The word fissure represents a large proportion of the data. 



