Large exploitations of two types of rock occurred: gypsum and calcareous rock.

The gypsum was exploited in the north and east of Paris: 10th, 18th, 19th and 20th arrondissements, these gigantic exploitations were conducted in areas where the depth of the quarry ceiling often reaches 10 meters. These quarries were often exploited with disregard to the most basic security measures. The quarries also held another danger: gypsum is water soluable and each infiltration of rain water washes away a little bit of the floors of these zones.

None of these exploitations continue today. They were all terminated "like lightening", thanks to the canon powder that was disposed of in the support columns.

But, it was the calcareous rock quarries that were the most heavily exploited. However of the 3150 hectares of exploited area in the Paris quarries (40% of the total surface area of Paris), these exploitations represent only 65 hectares.

Resulting from these old exploitations, there remains today 770 hectares of empty space in the form of inspection galeries and empty places under private properties. There are 135 kilometers of galeries: 91 under streets and 44 under gardens and other public buildings. 150 kilometers are under private domains. In total, almost 300 kilometers (2 times the distance of the metro lines). The inspection galeries are spread out as follows:

XIIth arrondissement : 200 meters
XVIth arrondissement (Chaillot quarries, Passy network) : 7 kilometers
XIIIth arrondissement : 25 kilometers
The large XIVth arrondissement network (XIVth, northern XVth, Vth, VIth) : 100 kilometers

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