The colors used on most original maps are not pleasing, a fact that is of no particular importance, but--and this is of importance--they often fail to give clear distinctions; the separate areas can not always be identified or distinguished with certainty. Again, some colors are fugitive, and when laid on in light tints they disappear entirely or become uncertain. Much of the difficulty in identifying and discriminating colors on an author's original maps is due to the promiscuous mixing of colors. Many persons can not match or discriminate mixed or broken colors. Hence if the supply of a color produced by mixing becomes exhausted and the attempt is made to duplicate it by a second mixture the two will probably fail to match. It is therefore suggested that colors in full strength and colors diluted to half strength be used instead of mixtures of two or more pigments, so that one color in two strengths or tones can be employed to indicate areas that are to be distinguished. The colors listed on page 26 will give 24 satisfactory distinctions and will thus supply all demands for map coloring. To insure satisfactory contrasts between colored areas on a map, unlike colors should be placed next to each other--that is, colors should be placed together that are widely separated in the spectrum, such as yellow and mauve, red and green, blue and orange, burnt sienna and olive-green; not such as red and orange, blue and purple, orange and yellow, sepia and burnt sienna. A sufficient quantity of water and color pigment to be used for one formation area on a map should be stirred in a saucer until the desired tint is produced before it is applied. To maintain the same tone properly the color should be well stirred every time the brush is filled; if it is not stirred the brush will on the next dipping take up a lighter tint, because most pigments, especially those derived from minerals, tend to precipitate. When the colors are applied the map should preferably be placed in a slightly inclined position, and the coloring should be started at the upper boundaries of an area to be colored, the well-filled brush being pulled toward the painter and Worked rapidly back and forth horizontally, the edges of the fresh color being kept wet. If the edges are allowed to dry, a hard line and a smeared or uneven effect will be produced. A strong color should generally be used for small areas unless the map shows also large areas that must have the same color; lighter hues should be used for large areas. Bright colors are best suited for areas of igneous rocks, dikes, and veins, and these may be reduced in strength for the larger areas.