Geological section (through the southern edge of the Paris Basin showing the layout of the Tertiary formations and the extent of the various silicified facies. Almost all sand and limestone formations contain zones of silicification. They are particularly well developed in limestones on the wide monoclinal structure of the Brie Plateau. Data source: National geological data bank (BSS-BRGM, InfoTerre, 2023), geological maps at 1:50,000 and their notes, and personal field observations and drill core descriptions. See trace F-G of the section on Figure 1.