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In the first chapter, the author presents alL the geothermal data available from the "Archives de la Carte Géologique"by the Geological Survey of Belgium. The check-lists give firstly the localisation; afterwards, the data about the depth, the temperature in °C and the concerned geological formation; at last, the geothermal gradients (main, at intervals, and the mean).

The second chapter is dealing with the transformation of the data for further comparison. The uniformised data are used along the third chapter, making a set of sketch maps. It appears that the mean geothermal gradient is of 1 °C each 33 m only to the depth of 1500 rn below the sea-level; downwards, it should become shorter.

This value is only a mean. Indeed, the "colder" areas of the Ardenne and the "Massif du Brabant" (older Paleozoic basement) contrast with the "warmer" areas of the Kempen and the Haine - Sambre - Meuse ridge (younger Paleozoic basement). Some distorsions of the geothermal flux yielded because of the flow of the fresh, brackish or briny, underground waters would not be neglected.