274 REPORTS ON THE STATE OF SCIENCE, ETC. 



Geothermal Phenomena and Geological History with Special 

 Reference to Old Structures in Geothermal Equilibrium. 



By M. W. Strong. 



Journal of the Institution of Petroleum Technologists, vol. 16, no. 86, 1930, 



pp. 889-901. 



Geothermal phenomena are discussed in this article under the following 

 headings : 



1. Introduction. — Thermal conditions to be expected in old structures 

 are considered first. Investigation is continuing with reference to these 

 conditions in young structures where thermal changes may be expected to 

 be still continuing. 



2. Some factors affecting geothermal distribution. — The conductivity of the 

 rocks and of their fluid contents are the dominant factors determining the 

 thermal conditions. Topographic irregularities must also be taken into 

 consideration. Effects due to the underground movement of water, oil, 

 and gas must be analysed specifically in each case in which they arise. 



3 . Conductivities of rocks. — Approximate conductivities of various rocks 

 and substances are given. 



4. Influence of thermal conductivity of strata on isogeotherms .—The 

 distribution of heat in and around masses of relatively good and bad 

 thermal conductivity placed in a medium through which heat is flowing is 

 examined by the aid of some diagrams. 



5. Buried hills or anticlinal structures. — These are considered on the sup- 

 position in each instance that the structure is old enough for geothermal 

 equilibrium to have been attained. 



6. Faults and unconformities. — The distribution of isogeotherms in the 

 neighbourhood of a fault which has thrown badly conducting strata against 

 strata of higher conductivity is considered. 



7. Buried faults and unconformities. — The thermal distribution above a 

 buried fault by which beds of different conductivities have been brought 

 into contact, the whole lying buried beneath a thick overburden, is 

 considered. 



8. Importance of conductivity determination. — Determination of the con- 

 ductivities of the beds should be one of the first objectives of a geothermal 

 survey, as they are the controlling factors determining the geothermal 

 distribution. 



9. Note on topography and isogeotherms. — The static distribution of 

 temperature under hills is illustrated in a figure. It is shown by the 

 diagrams that in homogeneous horizontal strata topographic irregularities 

 alone would give rise to irregularities of the isothermal contours. 



10. Factor for elevation with respect to sea-level. — The necessity of 

 measuring the mean surface temperature is mentioned. 



11. Influence of dip on conductivity. — In some sandstones, especially if 

 micaceous, and in slates and some laminated shales, the conductivity per- 

 pendicular to the cleavage may be only about half that parallel to the cleavage 

 so that in some districts allowance must be made for this additional factor. 



12. Some general remarks on static thermal fields are given. 



13. Presentation of geothermal data. — It is evident that for the elucidation 

 of geothermal data the data must be presented in the form of isogeotherms 

 drawn on a geological section, together with information regarding the 

 lithology of the several beds. 



14. Gradients and their significance. — Wide variations in the values of 



