The Getty-Dooley well No. 7 was drilled in Eddy County, New Mexico, to a depth of 6,683 feet and passed through a thick section of Permian rocks, including the Rustler, Salado, Carlsbad, Capitan, Delaware Mountain, and into the top of the Bone Spring limestone. This stratigraphic section is divisible into three lithologic units: the Rustler-Salado, the Carlsbad-Capitan, and the Delaware Mountain unit. The subnormal geothermal-gradient curve for this well is also divisible into three parts and these subordinate gradients coincide with the lithologic divisions. Other possible factors that might cause the fundamental variations in the geothermal-gradient curve, such as water, heat reactions from solution, igneous intrusions, and radioactivity, are found wanting to explain th character of the curve. The radioactive heat of potassium is also found insufficient to affect the gradients in the Permian basin. It is therefore concluded that this subnormal geothermal-gradient curve owes its form to the different conductivities of the successive layers of rock.