You are a geologist. While walking in the fog one day, you bang into a cliff. After rubbing your sore nose, you inspect the clif
f, and see what is shown in the picture, in a one-foot-square area. You recognize that this cliff is made of “fossil sand dunes”, with wind-blown sand that was later glued together by hard-water deposits. You are accompanied by a student, who is carrying your tea and crumpets for you. You sketch four arrows on the cliff, label them as shown, and ask the student which of the arrows was pointing up when the loose sand was deposited. Your student is brilliant, and correctly tells you the answer. The arrow that was pointing up when the loose sand was deposited is the arrow that is closest to:
