ORIGIN OF MOUNTAIN RANGES. 563 



by tension. But there would inevitably come a time when the 

 surface being substantially cool and moreover receiving heat also 

 from the sun, its temperature would be fixed or nearly so, while 

 the incandescent interior would be still cooling and contracting. 

 Such has probably been the case ever since the commencement 

 of the recorded history of the earth. The hot interior now 

 cooling and contracting more rapidly than the cool crust, the 

 latter following down the ever shrinking nucleus would be thrust 

 upon itself by lateral pressure with a force which is simply 

 irresistible. If the crust were ten times, yea one hundred times 

 more rigid than it is, it must yield. It does yield along the lines 

 of greatest weakness, i. e., along marginal sea-bottoms as already 

 explained. As a first attempt at a physical theory, it seems 

 reasonable, and therefore, until recently, has been generally 

 accepted. 



OBJECTIONS TO THE CONTRACTIONAL THEORY. 



It is well known that American geologists have taken a very 

 prominent part in the study of mountain structure and mountain 

 origin. So much so indeed that the lateral pressure theory in the 

 form given above and interior contraction as its cause, have some- 

 times been called the "American theory." It is also well known 

 that my name, among others, especially Dana's, has been associ- 

 ated with this view. All I claim is to have put the whole subject, 

 especially the formal theory, in a clearer light and more consist- 

 ent form. T The formal theory I regard as a permanent acquisi- 

 tion. The contractional theory may not be so. It is natural, 

 from my long association with it, that I should be reluctant to 

 give it up. But I am sure that I am willing to do so if a better 

 can be offered. We all dearly love our own intellectual child- 

 ren, especially if born of much labor and thought ; but I am sure 

 that I am willing, like Jephtha of old, to sacrifice, if need be, this 

 my fairest daughter on the sacred altar of Truth. Objections have 

 recently come thick and fast from many directions. Some of these 



1 " Theory of the Formation of the Great Features of the Earth's Surface." Am. 

 Journal, Vol. 4, pp. 345 and 460, 1872, and also "Structure and Origin of Mountains," 

 Vol. 16, p. 95, 1878. 



