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Author: Dupuis (1988).

Description: this marine unit contains, from base to top, three units:

- a grey, sandy, smectite clay, poorly calcareous and glauconiferous, with some peb-bles;

- green, very glauconitic, clayey sands, with some marl layers; disseminated pebbles are present. Polymorphina are frequent, few lamellibranchs and gasteropods occur;

- marls, lithified calcareous marls, grey or yellowish, glauconiferous limestone, with detritic quartz grains and pebbles. Foraminifera, gasteropods and lamellibranchs occur frequently, sometimes abundantly.

Stratotype: for the first time described as the "Heersien" in the "Brasserie Paternostre" borehole at Mons (Delvaux, 1877). Sheet 45/7-8 (Mons - Givry). Co-ordinates: x = 120.32, y = 126.44, z = +31 m. The formation is most complete in borehole no. 7 of the "Charbonnage du Hainaut" (1918) between 65.5 m and 97 m depth (incomplete core recovery) (Saint-Ghislain 138, in Marlière, 1969). Sheet 45/5-6 (Quièvrain - Saint-Ghislain). Co-ordinates: x = 108.90, y = 128.15, z = +24 m.

Area: deepest parts of the Mons Basin, only known from boreholes.

Members: the formation is not subdivided into members.

Thickness: probably not more than 40 m.

Age: Thanetian.

Remarks: the formation is also discussed by De Geyter (1981), Delvaux (1877), Du-puis & Robaszynski (1986), Cornet (1927), Maréchal (1993), Marlière (1969), Moorkens (1982) and Robaszynski (1978).