2 Clarence King — Age of the Earth. 



to test the probable truth of many cases of earth-temper- 

 ature distribution ; at least so far as to justify the rejec- 

 tion of such as involve considerable liquidity of the upper 

 couches. In an earth of which the superficial quarter of 

 radius is composed of materials that contract from the fluid 

 condition toward and in the act of congelation, any tempera- 

 ture gradient in which the downward heat augmentation 

 exceeds the rate by which advancing pressure raises the fusion 

 point, would obviously reach a fused couche, and all such dis- 

 tributions may be rejected as violating the requirements of 

 rigidity. 



A recent investigation of the rock diabase in its relations to 

 heat and pressure offers the formerly lacking means of testing 

 the admissibility of many cases of earth- temperature distribu- 

 tion from the point of view of solidity. Ten years ago in a 

 laboratory established by me in connection with the United 

 States Geological Survey, Dr. Carl Barus began a series of 

 experimental researches tending toward the solution of some 

 of the unknown but important points of geological physics. 

 It has been my privilege to indicate the direction of much of 

 the inquiry. The understanding between us maintained his 

 entire independence in the mode and prosecution of the inves- 

 tigations and secured for him the fullest responsibility and 

 credit for the purely physical results, many of which have at 

 intervals appeared in this and other journals. For myself was 

 reserved the privilege of making geological applications of the 

 laboratory results. One of the most important of these is Dr. 

 Barus's lately completed determination of the latent heat of 

 fusion, specific heats melted and solid, and volume expansion 

 between the solid and melted state, of the rock diabase.* To 

 him I am also very generally indebted for aid in considering 

 the present problem. 



Diabase was chosen by me as fairly illustrative of the prob- 

 able density and composition of the surface "03 or - 04 of the 

 earth's radius. For Laplace's law of distribution, density at 

 the surface is taken at 2'75 and down one-tenth of radius at 

 3*88, yielding a mean density of the whole tenth of 3 '33 and 

 for the upper five-hundredths of about 3. For the whole 

 tenth a rock like the extremely heavy basalt of Barensteinf 

 (sp. gr. 3*35) would approach closely a fair mean expression of 

 density. Typical hornblende-andesite comes closest to the 

 average density at the surface, but diabase (sp. gr. 2 8 to 3 1 ), 

 nearly enough fills the conditions of the shell which this 

 study seeks to investigate. The particular diabase under 

 examination came from Jersey City, and was taken from the 

 immediate vicinity of the Pennsylvania R. E, cut. 



*This Journal, Dec, 1891, and Jan., 1892. 

 f J. Roth, Gesteins-Analysen, 1861, p. 46. 



