Figure 127: White Cliffs. An extensive layer of limestone is exposed on both sides of the English Channel: in the cliffs of Normandy, France (top) and the White Cliffs of Dover, England (bottom). This 600–1,000-foot layer extends under the Channel and into England and France. Was this region, and others like it, a shallow sea that slowly accumulated limestone or did the limestone come from subterranean water chambers? Answering this question will provide insight on the geologic history of the entire earth.