Figure 150: White Cliffs. An extensive layer of limestone is exposed on both sides of the English Channel: in the cliffs of Normandy, France (left) and the White Cliffs of Dover, England (right). This 600–1,000-foot layer extends under the Channel and far into England and France. Was this region a shallow sea that somehow accumulated all this limestone, or did the chemistry for this limestone originate in the subterranean water chambers by an understood process? Answering this question will provide insight on the geologic history of the entire earth—and much more.