Shaler.] 10 [June 6, 



induced by the extreme heat of that point, then we must suppose that 

 cooling went on until the whole mass was reduced to something like 

 an equal temperature throughout, and the whole sphere become solid 

 at once. During this process of cooling down, successive crusts might 

 be formed, but they would necessarily be transient phenomena, break- 

 ing to pieces as soon as they began to attain considerable thickness.* 



This last supposition seems 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 tempera- 

 ture 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 surface before any part 

 became rigid. On this account we are driven to adopt the other 

 view as the more probable, and regard the superficial 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 incon- 

 siderable thickness, that the surface might also begin to solidify, and 

 the intervening igneous matter being in a state of viscous fluidity, 

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

 and foil into the fluid below. The further solidification of the inte- 

 rior 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 sxir- 

 faces 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 parser Is to show some 

 reasons for believing that both of these phenomena may be exiilalned 



* See the Preliminary Observations to the Paper of Hopkins above referred to, 

 where these considerations will be found. 



