How does a ditch become a hill?

The geological history of an environment is filled with new developments. There, where in the past mountains arose, only plains now remain... There, where a lake spread across, a ditch appeared, which then turned into a hill.
This is the case of the Colline de Perréal hill which was built up in four phases...
- through the depositing of different rocks,
- these fractured and then caved in at the centre,
- erosion them wore them down, planing down the high edges
- and the central portion progressively started standing out...
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