THE MOUNTAIN FRAMEWORK. 115 



control. When it leaves a body contraction ensues, and the 

 strength of this tendency can not be resisted by any means in 

 our power. Loss of heat is always attended by contraction 

 except when the temperature is a few degrees above that at 

 which the body passes from the liquid to the crystalline solid 

 state for there is a certain critical point at which reduction 

 of temperature begins to be accompanied by expansion, until 

 the solid condition is attained; after which further reduction 

 is attended again by contraction. 



Now, ever since Leibnitz, two hundred years ago, enun- 

 ciated his theory of a once molten earth, geognostic students 

 have been considering what must be the natural course of 

 events in the cooling of such a globe. Constant Prevost ad- 

 vanced a suggestion sound in theory and fruitful in conse- 

 quences. That molten globe, he said, must have become ] 

 incrusted. By degrees the crust would thicken, and the trans- 

 mission of heat from the interior would be retarded. By and \ 

 by, the radiation of heat from the exterior would become 

 diminished to such an extent as to just equal the heat received 

 at the surface by transmission through the crust. That is, a 

 constant temperature would exist at the surface of the earth 

 a constant temperature at the mid-zone in the crust. But the 

 interior would still continue to lose heat through the crust, 

 though the crust retained a uniform temperature. It the interior 

 did not supply heat to the crust, the latter would grow colder. 



So the interior, in consequence of loss of heat would con- \ 

 tract ; but the crust, losing no more than it receives, would 

 not contract. That is, the crust would become too large for 

 the shrunken nucleus. What would result? Do you con- 

 ceive that the crust would rest raised above the nucleus, 

 leaving vacant, or even steam-filled spaces between the two ? 

 Remember the enormous weight of the atmosphere fourteen 

 pounds on every square inch. Remember the enormous weight 

 of the crust, and the utter impossibility of its sustaining the 

 strain of bulging ver a vacuum of one, ten or a hundred 

 miles. Assuredly, the crust must settle down as fast as the 

 molten nucleus grows smaller. 



