rica runs a long and tortuous course, but finally closes
back on itself, so will every contour do likewise. And just as
truly as every bend in that high-tide mark turns out around a
promontory, or in around a bay, so will every bend in a contour
stand for a hill or a valley, pointing to the lowlands if it
be a hill, and to the height if it mark a valley.

If the map embrace a whole continent or an island, all the contours
will be of closed form, as in figure 11, but if it embrace only
it part of the continent or island, some of the contours will be
chopped off at the edge of the map, and we have the open form
of contours, as we would have if figure 11 were cut into two
parts.

The closed form may indicate a hill or a basin; the open form,
a ridge or a valley; sometimes a casual glance does not indicate
which.

Take up, first, the contour of the open type. If the map shows
a stream running down the inside of the contour, there is no
difficulty in saying at once that the ground feature is a valley;
for instance, V, V, V, and the valley of Corral Creek on the
map. But if there is no stream line, does the contour bend show
a valley or a ridge?

First of all, there is a radical difference between the bend
of a contour round the head of a valley and its bend round the
nose of a ridge,

Compare on the map the valleys V and the ridges R. The bend of
the contour round the head of the valley is much sharper than
the bend of the contour round the nose of the ridge. This is a
general truth, not only in regard to maps, but also in regard
to ground forms. Study any piece of open ground and note how
much wider are the ridges than the valleys. Where you find a
"hog back" or "devil's backbone," you have an exception to the
rule, but the exceptions are not frequent enough to worry over.

To tell whether a given point is on a ridge or in a valley, start
from the nearest stream shown on the map and work across the
map to the undetermined point, keeping in mind that in a real
trip across the country you start from the stream, go up the
hill to the top of a ridge, down the other side of the hill to a
water-course, then up a hill to the top of a ridge, down again,
up again, etc. That is all traveling is--valley, hill, valley,
hill, valley, etc., though you wander till the crack o' doom.
And so your map travels must go--valley, hill, valley, hill--till
you run off the map or come back to the starting point.

On the map, follow the