The Survey's color scheme (see p. 63) need not be applied at this stage of preparation, except in the most general way. Appropriate final colors can be best selected when the new map is made ready for engraving. In the author's original maps adequate color distinctions between areas are more important than the use of standard geologic colors. Patterns should not be ruled in one color on an original map to indicate distinctions between different formations of the same age or period, because such patterns are difficult to produce by hand with proper uniformity except by engraving. It is of vital importance that an original base map should be free from colors and from technical symbols in order that it may be kept clean for photographing and preserved for possible future use. Such a map should preferably be photographed in order to obtain prints on which to add the colors and symbols; the use of an oversheet for this purpose is not nearly so satisfactory. When photographed a base map should be reduced to publication scale in order to save the additional cost of a larger negative, and this reduced map may be made up for publication by the addition of colors and symbols, title, explanation, etc.; but the lithographer will also need the original base map from which to make his reproduction. DIAGRAMS. ESSENTIAL FEATURES. The term "diagrams," as used here, includes such illustrations as mine plans, profiles, sections, stereograms, and maps that are more diagrammatic than cartographic. The first essential in the original drawings for simple diagrams is clearness of copy. Simplicity of subject does not warrant hasty preparation, for an original sketch that has been carelessly drawn and is inaccurate or inconsistent in detail may lead to serious errors. Ruled paper printed especially for platting profiles and cross sections should be used. Curves or graphs made by an author with pencil on blue-lined section paper may be inked by more skillful draftsmen. An author's pencil sketches are usually satisfactory if they indicate plainly the facts to be represented, but they should be prepared with some care as to detail. Tables and like matter are not generally satisfactory material from which to prepare drawings. In drawings for diagrams that are to be printed in the text as figures the use of large, solid black bars or of conspicuous areas of solid black is objectionable, because the black is likely to print gray and to appear uneven in tone. Ruled tints or cross lining give better effects. Stereograms should be prepared by an author with especial care, for they represent facts only as the author sees them, and the author's view must be imparted to the draftsman graphically. The "third dimension"--the relief--in such drawings is not easily expressed and should be brought out clearly in the author's rough sketches.