Newly measured heat flow and full heat production determinations over the Armorican Massif, Western France, are tested against a linear relationship as proposed through Birch's law. The data do not fit a strict linear relationship but are within an elongated cluster which can be approximated (in mW/m2 and km) by: Q=26.6 (¿3.5)+15.6 (¿0.6) * A

These parameters are compared with those of surrounding Hercynian regions. Data from the Central Massif and previously failed to fit any linear relationship. Data for Scotland and Southern England could not be fitted to a single line. However, the present data and those from Southern and Central England do fit a single line, suggesting that the three regions form a single geothermal province. The depth parameter is greater than the root depths of the granitic plutons, indicating that heat sources can exist at depths below the granitic intrusions. The deep crustal structure revealed from seismic studies agrees with the radiogenic elements distribution deduced from thermal data. ¿ American Geophysical Data