We measured the length of the Grand Canyon by the length of the river
running through it, but the running extent of wall can not be measured
in this manner. In the black gneiss, which is at the bottom, the wall
may stand above the river for a few hundred yards or a mile or two; then
to follow the foot of the wall you must pass into a lateral canyon for a
long distance, perhaps miles, and then back again on the other side of
the lateral canyon; then along by the river until another lateral canyon
is reached, which must be headed in the black gneiss. So for a dozen
miles of river through the gneiss there may be a hundred miles of wall
on either side. Climbing to the summit of the black gneiss and following
the wall in the variegated quartzite, it is found to be stretched out to
a still greater length, for it is cut with more lateral gorges. In like
manner there is yet greater length of the mottled (or alcove) sandstone
wall, and the red wall is still farther stretched out in ever-branching
gorges.
To make the distance for ten miles along the river by walking along the
top of the red wall it would be necessary to travel several hundred
miles. The length of the wall reaches its maximum in the banded
sandstone, which is terraced more than any of the other formations. The
tower limestone wall is less tortuous. To start at the head of the Grand
Canyon on one of the terraces of the banded sandstone and follow it to
the foot of the Grand Canyon, which by river is a distance of 217 miles,
it would be necessary to travel many thousand miles by the winding way;
that is, the banded wall is many thousand miles in length.