Fantômes de roches.....

L'altération de type " fantôme de roche " : processus, évolution et...

For several years, numerous examples of ghost rocks have been recognised in karst areas in Belgium, in France and in Italy. They correspond to decalcified pockets but also to decalcified corridors filled with in-situ alterite. It is a special case of karstification where a non-soluble skeleton remains and preserves the structures of the initial rock (fossils, joints, levels of cherts, etc.).

http://geomorphologie.revues.org