Sandstone or limestone? How about both?

The Roc de Chère is made up of two main types of rock: limestone and sandstone.

Sandstone is a sedimentary rock composed of sand, or more precisely silica. It erodes easily and yields a grey sand that is highly acidic, which you may have seen at the most recent viewpoint.

The vegetation that grows on the sandstone has evolved to tolerate such acidity. It bears a striking resemblance to the vegetation of the Fontainebleau forest, which also grows on sandstone.

Because sandstone is an impermeable (waterproof) rock, you'll see the Roc de Chère fill up with more than 30 temporary puddles from autumn to spring.