On the Formation of Mountain Chains* 513 



This last supposition seoms to be excluded by the well-known 

 fact of the increase of temperature as we go from the surface 

 towards the centre; the rate of increase is such that we would 

 attain a temperature sufficient to melt the most refractory substances 

 in a few miles from the surface ; this is far from the state of things 

 we would expect to find if the whole interior had been reduced to 

 the temperature at which solidification could take place at the sur- 

 face before any part became rigid. C)n this account we are driven to 

 adopt the other view as the more probable, and regard the super- 

 ficial portions as the last to become solid, and the centre as the first 

 rigid portion of the earth. 



As solidification advanced from the centre towards the surface, 

 there would be a time when the remaining liquid matter was of in- 

 considerable thickness, that the surface might also begin to solidify, 

 and the intervening igneous matter being in a state of viscous fluid- 

 ity, might so far uphold the solid outer crust, that it would not break 

 up and fall into the fluid below. The further solidification of the 

 interior would then take place in two directions outward from the 

 central nucleus, and inward from the outer crust. If, however, this 

 residual fluid matter was confined, beneath, say, one hundred miles 

 of crust, cooling would proceed with such extreme slowness, that a 

 very great time might elapse before it became lost in the already 

 solidified surfaces above and below. It is not impossible that to 

 this insignificant relic of an original molten condition, we owe all 

 the phenomena of igneous action which have affected the crust since 

 the beginning of the geological record. 



There seems no point of conflict between this conception and those 

 conclusions of geologists which are supported by any considerable 

 amount of evidence ; it only contravenes those hypotheses which 

 have failed when subjected to critical examination, or which from 

 their essentially undemonstrable character can not be either verified 

 or disproven. At first sight it might seem difficult to account for 

 the phenomena of corrugation of the earth's crust, as exhibited in the 

 continental folds, and in mountain chains, if we reject the hypothesis 

 of internal fluidity. The design of the present paper is to show some 

 reasons for believing that both of these phenomena may be explained 

 without the assumption of anything more than the trifling amount 

 of igneous fluidity involved in the hypotheses we have just discussed. 



Without any particular examination of the facts, it seems to have 

 been assumed by most geologists that all the phenomena of corruga- 

 tion, whether exhibited in mountain ranges, or in continents, are to 

 be regarded as effects of one and the same cause, differing only in 

 magnitude. It is manifest that it is a matter of first importance in 

 seeking an explanation of the origin of these phenomena, to deter- 

 mine whether this assumed identity of cause is true or no. If it be 

 the fact that continental elevations and mountain elevations are but 

 degrees of effect of the same cause, then there should be no other 

 differences in the phenomena than those of magnitude, or of features 

 dependent directly upon the magnitude of the areas involved in the 

 disturbance; furthermore there should be something like a series, at 



