1. Caves form in karstic regions.

2. The sensitivity perimeters as defined for the alluvial layers should be applied to the karstic and non-karstic zones surrounding underground habitats which warrant protection or are endangered.

3. The accumulated sediments in the karstic caverns derive from the periodic inwashing of the insoluble residues built up on the surface of erosion, were indurated after the sealing of the karstic openings with calcareous muds during the Ordovician transgression, and were faulted with their cover when the Saguenay graben formed.

4. So karstic regions are areas of the world where the infiltrating water along cracks, fractures, can easily dissolve soluble lithologies, forming a drainage system of tunnels, conduits -- a three-dimensional network, actually.

5. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward.

6. In (1), particular attention is paid to the geotechnical properties of karstic rocks and also of associated material, loose and coherent, grouting and watertightening, the safety measures required because of the influence of foundation works on underground water and slope stablity.