PROCEEDINGS 



OF 



THE ROYAL SOCIETY. 



" On Underground Temperatures ; with Observations on the 

 Conductivity of Rocks ; on the Thermal Effects of Satura- 

 tion and Imbibition; and on a Special Source of Heat in 

 Mountain Ranges." By Joseph Prestwich, M.A., F.R.S., 

 F.G.S., &c. Received January 24. Read February 12, 1885. 



Page 



1. Introduction — Historical Review 1 



2. G-eneral Observations 6 



3. On Observations in Coal Mines 9 



4. On Observations in Mines other than Coal 25 



5. On Observations in Artesian Wells and Bore-holes 35 



6. On Observations in Mountain Tunnels, and on a Special Source of Heat in 



Mountain Ranges 43 



7. On the Conductivity of Rocks ; and on their Saturation and Imbibition . . 47 



8. Conclusions 53 



Page 



L Table. General List 56 



II. Table. Coal Mines 88 



III. Table. Mines other than Coal 96 



IV. Table. Artesian Wells and Bore-holes .... 106 



1. Introduction. 



The opinions of physicists and geologists as to what may he the 

 probable thickness of the crust of the Earth differ very materially. 

 On the strength of its great rigidity and the absence of tides, 

 physicists contend for a maximum thickness and the comparative 

 solidity of the whole mass of the globe. On the evidence of volcanic 

 action, the crumpling and folding of the strata in mountain ranges, 

 its general flexibility down to the most recent geological times, and 

 the rate of increase of temperature in descending beneath the sur- 

 face, geologists contend for a crust of minimum thickness (although 

 respecting the measure of this there is great difference of opinion) 

 and a yielding substratum, as alone compatible with these phenomena. 



My intention here is not to enter upon the general question, but to 

 lay before the Society the results of an inquiry on one section of it 

 — namely, the rate of increase of temperature beneath the surface, — a 

 subject equally affecting the argument on both sides. My attention 

 was more specially directed to this subject in connexion with an 

 inquiry on the cause of volcanic action, during which I found that 

 the recorded observations gave so wide a choice in the selection of a 

 mean rate for the increase of temperature, or as termed by Professor 

 Everett, the " thermometric gradient," that very different values might 



VOL. XLI. 6 



