THERMAL CONDUCTIVITIES OF ROCKS 267 



Empire-Star mine, Grass Valley, Nevada County, are given in a table. 

 According to this table the following values of the reciprocal gradients were 

 established : 



From 500 to 1,280 ft., i° F. for every 168 -6 feet 



to 2,400 ,, i° F. „ 175 • 8 „ 



to 3,200 ,, i° F. „ 186 • 1 „ 



to 3,700 „ i°F. „ 189-8 „ 



A comparison of temperatures in various deep mines is given in another 

 table, according to which the thermal gradient at Grass Valley is in close 

 agreement with the thermal gradient at the Mother Lode, California, 

 slightly exceeds the gradient in the Rand, South Africa, and is much less than 

 the gradient in the Michigan copper mines and in the St. John del Rey 

 mine, Brazil. 



In a footnote Johnston says, ' In A. Knopf's article, " Mother Lode System 

 of California " (U.S. Geol. Survey, Prof. Paper 157, pp. 22-23, 1929), a 

 gradient of i° F. for 150 ft. is given. These data have been recalculated by 

 the method of least squares by H. C. Spicer, who obtained a reciprocal 

 gradient of 192-3 ft. per degree Fahrenheit from observations between the 

 depths of i,S75 an d 4, 200 ft. Knopf's values for the Central Eureka and 

 the Kennedy mines apparently are based on an assumed value of the mean 

 annual temperature Y of the air.' 



Geothermal Gradient of the Mother Lode Belt, California. 



By Adolph Knopf. 

 Journal of the Washington Academy of Sciences, Washington, D.C., vol. 22, 



no. 14, 1932, pp. 389-390- 



In this article Knopf offers the following objections to the conclusions 

 contained in W. D.Johnston's article ' Geothermal Gradient at Grass Valley, 

 California ' (see the previous article), pointing out two fundamental errors 

 made during the recalculation of the geothermal gradient at the Mother 

 Lode, made by Spicer : ' In the first place temperature observations from 

 two mines (the Plymouth and the Kennedy) situated ten miles apart were 

 used to compute a gradient, but this procedure is not permissible, as the 

 gradients at the two mines are most likely to be different. In the second 

 place it was assumed that the collars of the shafts of the two mines are 

 at the same altitude ; the collar of the Kennedy shaft is approximately 

 1,430 ft., whereas that of the Plymouth shaft is about 1,100 ft. above sea level.' 



A reply in explanation of his conclusions is given by W. D. Johnston in 

 an article published in the same number of the Journal of the Washington 

 Academy of Sciences, pp. 390—393. 



Geothermal Measurements in the Boreholes of the Donetz Basin. 



By S. Kraskowski. 



Gerlands Beitrage zur Geophysik, Ergdnzungshefte der angewandten Geophysik, 

 Leipzig, vol. 3, no. I, 1932, pp. 9-28. 



In the autumn of 1931 the Central Scientific Institution of Geology and 

 Geophysical Prospection in Leningrad carried out an experimental thermo- 

 survey in the deep drill holes of the Stalin district in the Donetz Basin. 



The apparatus used by the geothermical section of the institution was 

 constructed by members themselves and consisted of a winch with steel- 



