THERMAL CONDUCTIVITIES OF ROCKS 273 



The comparative trend of isotherms, geologic strata, and ground surface is 

 shown on two vertical sections through the anticlinal structure of the 

 Eastside field. The results indicate that rock temperatures in this vicinity 

 are controlled chiefly by surface topography and thickness of sediments. 

 Definite correlation between relative temperatures and the oil-bearing 

 structure is not evident. 



Relationship between the Geothermal Depth Gradient and the Heat 



Conductivity of Rocks. 



By H. Borger. 

 Gluckauf, Essen, vol. 67, no. 17, 193 1, pp. 545-551. 



The article is divided into two chapters : (1) investigation of the influ- 

 ence of the heat conductivity of rocks upon the geothermal gradient, and 

 (2) heat conductivity of various rocks. 



From the investigations on the relationship between the heat conductivity 

 of rocks and the geothermal gradient the author draws the conclusion that 

 geothermal gradients have different values in different rocks deposited in 

 layers and that their ratio depends on the heat conductivity of the different 

 kinds of rocks. 



The numerical value of the geothermal gradient inside a certain type 

 of rock depends not only on its capability of conducting heat, but also on 

 the ratio of magnitude of rocks overlying one another. 



The author gives examples showing that in rocks, the geothermal gradient 

 of which is high owing to their good heat conductivity, the temperature 

 may be unusually high if the deposits overlying them have a lower heat 

 conductivity. The differences in heat conductivity of single types of rocks 

 are sufficient for the explanation of the unusually high temperatures often 

 observed in salt mines and coal mines, without the necessity of assuming 

 the existence of special sources of heat. 



The article is illustrated by four figures. 



Geothermic Measurements near Surface. 



By A. G. R. Whitehouse. 

 The Colliery Guardian, London, vol. 142, no. 3655, 1931, pp. 210-211. 



The object of the present observations was to study the relation of surface 

 air temperature to earth temperature at depths up to 30 ft., and to examine 

 the possibility of a more reliable datum for strata-temperature calculations. 



The observations were made at Edgbaston in the grounds of the University 

 of Birmingham at a point 453 ft. above Ordnance Datum. The earth 

 thermometers at depths of 1, 4 and 7 ft. were in gravel, the 30-ft. earth 

 thermometer being in soft sandstone. 



In Tables I and II are shown : Air and earth temperatures, annual means 

 for the six years, 1 924-1 929 ; and annual ranges of temperature of the 

 thermometers, respectively. 



From the results of this investigation the author shows that change in 

 mean earth temperature, with increasing depth near the surface, may be 

 distinctly erratic, and that mean air temperature shows no general relation- 

 ship to mean earth temperature near the surface. The author concludes 

 that, therefore, the only practical datum in this country for calculations of 

 geothermic gradient is the mean air temperature at the surface taken over 

 a long range of years, and that this datum is at the best a very rough one. 



