Evidence for a steepening of geothermal gradients in some deep mines and drill holes

Direct readings of rock temperatures taken along the line of the new Yates Shaft of the Homestake Mine disclose a geothermal gradient that steepens notably in depth. Comparison of these results with those from several other deep mines and deep drill holes suggests that this steepening may be a general effect to the depths penetrated by those mines and drill holes. A possible cause is a gradual decrease in thermal conductivity of rocks in depth due to a gradual decrease in the amount of intergranular moisture in the rocks.