show SLOPES. It has already been explained that
from any contour to the next one above it the ground rises a
fixed number of feet, according to the vertical interval of that
map. From the scale of distances on the map the horizontal
distance between any two contours can be found. For example:
On the map the horizontal distance between D and E is 90
yards, or 270 feet. The vertical distance is 20 feet the V. I. of
the map. The slope then is 20/270 = 1/13.5 = 7-1/2% = 4-1/2 deg., in all of
which different ways the slope can be expressed,

[Illustration]

On a good many contoured maps a figure like this will be found
in one of the corners:

[Illustration]

On that particular map contours separated by the distance

[Illustration]

on the vertical scale show a slope of 1 deg.: if separated by the
distance

[Illustration]

they show a 2 deg. slope. etc. A slope of 1 deg. is a rise of 1 foot in
57. To use this scale of slopes copy it on the edge of a piece
of paper just as you did the scale of distances and apply it
directly to the map.

You will notice that where the contours lie closest the slope
is steepest; where they are farthest apart the ground is most
nearly flat,

It has already been set forth how contours show height and slope;
in addition to this they show the shape of the ground, or GROUND
FORMS. Each single contour shows the shape at its particular level
of the hill or valley it outlines; for instance, the 880 contour
about the penitentiary shows that the hill at that level has a
shape somewhat like a horse's head. Similarly, every contour
on the map gives us the form of the ground at its particular
level, and knowing these ground forms for many levels we can form
a fair conception of what the whole surface is like.

A round contour like the letter O outlines a round ground feature;
a long narrow one indicates a long narrow ground feature.

Different hills and depressions have different shapes. A good
many of them have one shape at one level and another shape at
another level, all of which information will be given you by
the contours on the map.

One of the ways to see how contours show the shape of the ground
is to pour half a bucket of water into a small depression in
the ground. The water's edge will be exactly level, and if the
depression is approximately round the water's edge will also be
approximately round. The outline will look something like figure
6.

Draw roughly on a piece of