The effects of simple compression and wetting on the thermal conductivity of rocks

Measured thermal gradients in the Earth run from about 6° per km to 150° per km. Some of the differences may be due to differences in the rate at which heat is flowing toward the surface, but many of them result, doubtless, from differences in conductivity of the rocks through which the heat flows. Out of hundreds of gradient‐measurements, only about a dozen have been correlated with conductivity, and it is significant that in these cases the values obtained for the rate of heat‐flow differ from their mean value by only about 25 per cent, although the gradients themselves vary by a factor of four or five.