A Late Cretaceous (Maastrichtian) chalk in a quarry outside Maastricht, The Netherlands. This quarry face is an excellent example of fracture characteristics in reservoirs and aquifers. There are two size ranges of fractures and a major difference in fracture behavior of the chalk above and below the "surface" at about knee level on the man in the photo. The chalk below is intensely fractured, but the upper chalk is not. Note the major fracture (diagonal across the rock face) that connects upper and lower chalks - and could drain many of the small fractures. Photo by W. Ahr