On the Formation of Mountain Chains, 517 



dence, then the moment this latter action is effected, it is likely to 

 bring about fractures along shore linos, attended by the escape of 

 gaseous and igneous materials. This dislocation of the crust would 

 be attended by the pushing together of the superficial portions from 

 either side, and the resulting elevations might be complicated by the 

 intrusion of a greater or less amount of igneous matter. 



This view of the origin of mountain chains seems to be reconcil- 

 able with some of the most prominent features which are to be found 

 in their structure and distribution. Their usual, if not invariable, 

 origin along shore lines, the suddenness of their formation, the 

 variable amount of igneous action exhibited in their masses, are ex- 

 plicable on this hypothesis. On the other hand it is not to be 

 denied that some considerable objections can be urged against it. In 

 the first place, in order that any considerable elevation be formed by 

 this action, it would be necessary to have the upper and lower beds 

 slide one upon another, to a certain extent ; but it is to be borne in 

 mind that the power we are hypothecating is practically illimitable, 

 since it would, by the supposition, continue to accumulate until the 

 force became sufficiently great to overcome resistance. The sliding 

 of beds upon each other under the influence of great lateral pressure, 

 from the contraction of the lower portions of the crust, has fewer 

 objections to be urged against it than the view which assigns the 

 origin of mountain chains to the passage of great waves of trans- 

 lation through the crust, and their fixation by the intrusion of 

 molten matter. 



It is scarcely necessary for the author to state that no claim what- 

 ever is meant to be made in this paper to the hypothesis of the 

 origin of the features of corrugation of the crust from the influence 

 of contraction from loss of heat, one of the oldest and most gene- 

 rally accepted theories of the science. It having been denied by 

 very high authority that there existed any cause competent to pro- 

 duce lateral thrust, and thus to originate mountain chains, it has 

 seemed desirable to direct attention to the fact that the recession of 

 the isogeothermals would be attended by such lateral strain. 



The points which have been suggested in the foregoing consider- 

 ation, may be briefly summed up as follows : 



1. That the most probable hypothesis in the present state of our 

 knowledge of the earth, is, that it consists of an immense solid 

 nucleus, a hardened outer crust, and an intermediate region of com- 

 paratively slight depth, in an imperfect state of igneous fusion. 



2. That the continental folds are probably corrugations of the 

 whole thickness of the crust. 



3. That mountain chains are only folds of the outer portion of the 

 crust caused by the contraction of the lower regions of the outer shell. 



4. That the subsidence of ocean floors would, by producing frac- 

 tures and dislocations along shore lines, tend to originate mountain 

 chains along sea borders, and approximately parallel to them. 



[In connection with this subject, see also paper by the Rev. 0. Fisher, ante, 

 p. 493 ; also Delaunay, ante, p. 507.] 



