Terrestrial Heat Flow in

The average of twenty-six new heat flow determinations in the North Central area of the United States is 1.36±0.34 HFUt the values range from 0.90 to 2.2 HFU. Except for two determinations in Indiana, all of the measurements were obtained from continuous temperature-depth curves that were recorded in existing boreholes. With continuous temperature logs, we obtained very precise values of the geothermal gradient over short intervals, measured the thermal con-ductivity on a few samples for these selected intervals, and obtained precise values for the heat flow. Although all the stations are located in the stable continental interior, there are two distinct regions both on the basis of physiography and on the basis of heat flow. The Interior Lowlands is characterized by a regional value of 1.4 HFU, whereas the regional value for the Norther