8 Clarence King — Age of the Earth. 



The value of the integral and the surface rate for any 

 gradient does not change if conductivity and age vary 

 reciprocally, and the surface rate does not change if the 

 initial excess of temperature varies at the same rate as the 

 square root of the product of conductivity and the time of 

 secular cooling. If the square root of the product of conduc- 

 tivity and age be increased any number of times arid the depth 

 also be increased the same number of times, temperature 

 remains unchanged if the initial excess is unchanged, but if 

 the initial excess changes, temperature will change in the same 

 ratio. 



Upon the chart are delineated two families of temperature 

 distributions. Those in continuous lines, lettered a to f, are 

 calculated in accordance with the maximum surface rate of 

 50*6 ft. to 1° Fahr., being the generally accepted rate at. the 

 time Kelvin's curve was published. Those in dotted line and 

 lettered g to i, are constructed for the rate of 75 ft. to 1° 

 Fahr. the smallest of the observed inland rates. It is the 

 value given by Hal lock* for the recentty completed boring 

 near Wheeling, W. Ya. The last published value as reduced 

 from all available data by the B. A. committee is 64 feet to 1° 

 Fahr. It is, therefore, extremely probable that unless some 

 general but unrecognized cause, like a variation of temperature 

 due to the chemical action of hot water and progressive down- 

 ward either with heat or pressure, tends to raise or lower the 

 mean rate, the true surface distribution falls between the values 

 of 506 and 75 ft. per ° Fahr. upon which the two families of 

 gradients are based. 



The diabase line for melting temperature and depth D D is 

 traced from its superficial fusion point, 1,170° C. downward 

 according to the law established by Dr. Barns and expressed 

 in table 5. This is the special point of interest in the chart 

 and in the conclusions to which it gives rise. In passing from 

 this surface value of 1,170° G. through *1 of the radius, the 

 fusion temperature is raised to 6,139° C. ; continuing thence to 

 the center of the earth it reaches the surprising value of 76,200° 

 C. In consequence in an earth all of diabase any temperature 

 gradient having an initial excess of less than the above central 

 value must in reaching the surface either intersect the line D D 

 twice or fall wholly beneath it. Since this line represents melt- 

 ing temperature, any point vertically above it in the chart is 

 necessarily more highly heated than the melting temperature 

 for the same depth, and hence in fusion. Conversely, any 

 point below the diabase line being below the melting temper- 

 ature for that pressure and depth, falls into solidity. Thus 



*This Journal, vol. xliii, p. 234, 1892. 



