Contours also 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°, in all of which different ways the slope can be expressed. [Illustration: Slope.] On a good many contoured maps a figure like this will be found in one of the corners: [Illustration: Scale.] On that particular map contours separated by the distance [Illustration: Scale.] on the vertical scale show a slope of 1°; if separated by the distance [Illustration: |__2°__| ] they show a 2° slope, etc. A slope of 1° 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 paper a figure of the same shape and you will have a contour showing the shape of the bit of ground where you poured your water. Next, with your heel gouge out on one edge of your little pond a small, round bay. The water will rush in and the watermark on the soil will now be shaped something like figure 7. Alter your drawing accordingly, and the new contour will show the new ground shape.