Geomorphological settings. (a) Geological map of the Paris Basin. (b) schematic cross-section A-B through the superimposed plateaux. Quartzites occur in all sand formations intercalated between limestones armouring the plateaux. Trace C-D links to the section in Figure 2, trace F-G to the section in Figure 4, trace E-J extends the previous section to the borders of the basin and links to the section in Figure 24, and trace K-L links to the section in Figure 6.