River was flowing when the tilting commenced, and the upheaval was very slow, so that the river cleared away the obstruction to its channel as fast as it was presented, and this is the Grand Canyon. The rocks above were carried away by rains and rivers, but not evenly all over the country; nor by washing out valleys and leaving hills, but by carving the country into terraces. The upper and later-formed rocks are found far to the north, their edges standing in cliffs; then still earlier rocks are found rising to the southward, until they terminate in cliffs; and then a third series rises to the southward and ends in cliffs, and finally a fourth series, the oldest rocks, terminating in the Grand Canyon wall, which is a line of cliffs. There are in a general way four great lines of cliffs extending from east to west across the district and presenting their faces, or escarpments, southward. If these cliffs are climbed it is found that each plateau or terrace dips gently to the northward until it meets with another line of cliffs, which must be ascended to reach the summit of another plateau. Place a book before you on a table with its front edge toward you, rest another book on the back of this, place a third on the back of the second, and in like manner a fourth on the third. Now the leaves of the books dip from you and the cut edges stand in tiny escarpments facing you. So the rock-formed leaves of 91 V powell-canyons-57.jpg A GROUP OF STONE CORRALS. 92 powell-canyons-58.jpg RUINS. CLIFFS AND TERRACES. 93 these books of geology have the escarpment edges turned southward, while each book itself dips northward, and the crest of each plateau book is the summit of a line of cliffs. These cliffs of erosion have been described as running from east to west, but they diverge from that course in many ways. First, canyons run from north to south through them, and where these canyons are found deep angles occur; then sharp salients extend from the cliffs on the backs of the lower plateaus. Each great escarpment is made up more or less of minor terraces, or steps; and at the foot of each grand escarpment there is always a great talus, or sloping pile of rocks, and many marvelous buttes stand in front of the cliffs.