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 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.