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—and much more.