10 Clarence King — Age of the Earth. 



it follows that that depth nearly marks the original surface of 

 the solid nucleus and that the distance of 226 miles thence to the 

 surface measures the depth of the original couche of fusion. 

 Following the gradient toward the surface it is seen after 

 describing its great convexit}' in the fluid region to intersect 

 the diabase line a second time and enter a congealed shell or 

 crust formed by cooling a surface portion of the initial 

 fused couche, and leaving between the nucleus and crust, a 

 residual present shell of fusion of 200 miles from top to bot- 

 tom. The obvious tidal instability of a 26-mile crust resting 

 upon 200 miles of truly fluid magma is sufficient basis for the 

 rejection of this particular case of temperature distribution. 

 To fulfill the requirements of rigidity either the time of cool- 

 ing must be vastly greater to admit of entire congelation, or 

 the initial excess materially less. 



As an illustration of the first of these alternatives, gradient 

 c with the same initial excess as b (3900° C.) has been devel- 

 oped to complete solidity which on computation proves to have 

 required about 600xl0 6 years, at which time it has but just 

 reached tangency with the diabase line. Yet we are absolutely 

 precluded from accepting it as a probable case and assigning 

 OOOxlO 6 years as the age of the earth, because the temperature 

 values of its emergence at the surface fall below even the 

 75 feet to 1° Fahr. surface rate. Its emergence is at a rate of 

 •0081° Fahr. per ft. (124 ft. per ° Fahr.) which is far less than 

 the (Hallock) rate used in the clotted gradients, itself much 

 less than the accepted mean rate of the British Associa- 

 tion Committee. 



Gradient d, 1,950° C. initial excess, and 15xl0 6 years secular 

 cooling, falls still some millions of years short of solidity. 

 The initially fused surface couche w T as about Q6 miles in depth, 

 the present crust 38 miles thick and the present residual 

 fluidity of 33 miles depth from top to bottom. Here again 

 the liquid zone involves tidal instability and requires the 

 rejection of the line. 



Gradient e offers more satisfactory conditions : with an ini- 

 tial excess of 1,750° C, about the normal melting point of 

 platinum, and an age of 20x10" years, a condition is reached 

 which throws the convexity of the gradient below the diabase 

 line in complete solidity and fulfills all the conditions. Here 

 then is a possible age for an earth of diabase. Its initial sur- 

 face couche of fusion would have been about 53 miles and is 

 now wholly cooled into solid crust and united with the origi- 

 nal solid nucleus of compression. 



Gradient f, initial excess 1,230° C. and lOxlO 6 years secular 

 cooling, would in its first stage have shown only about five or 

 six miles of surface fusion which would very shortly have 

 cooled into solidity. 



