Land Office maps, scales and detail of. 14-15 Latitude, length of 1° of, at intervals of 10°. 91 Lending of photographs and drawings, rules governing. 34 Letter symbols, use of, on geologic maps. 20-21 Lettering, directions for. 53-55 for lithographing. 90 for names of streams. 52, 54 on diagrams. 64 on drawings of crystals. 70 on original maps. 19 on plans and cross sections of mines. 65-66 reduction sheet used in, plate showing. 54 use of type for. 54-55 Light, direction and gradation of. 66 Lithographs, printing and insertion of. 11 Lithography, original process of. 83-85 _See also_ Engraving on stone. Longitude, length of 1° of, at latitudes 0° to 90°. 91 M. Map of the world, millionth-scale, use of, for base maps. 14 Maps, areal patterns for, drawing of. 61-62 bar scales for. 59-60 base, conventional symbols used on. 45-46 including new data, how obtained. 13-14 indication of sources on. 13 of the United States on small scales, use of. 15 published maps available for. 14-17 reuse of, to be approved. 13 black and whits, patterns used on, plate showing. 62 borders for. 57-68 cultural features on. 52-53 enlargement and reduction of. 18 explanations for. 19, 58-59 geologic, details of, plate showing. 58 printing of. 87-89 standard colors for. 62-63 hydrographic features on. 61-52 lettering on. 53-65 materials used for drawing. 23-28 orientation of. 18 original, margin required on. 19 original base, amount of detail on. 17 must be free from colors and symbols. 28 preparation of. 13-14, 17-18 original geologic, method of coloring. 27-28 projection for. 18-19, 43-45 reduction or enlargement of, marking for. 63-64 relief on. 48-51 standard scales for. 18 symbols used on. 20-23 drawing of. 61 plates showing. 20, 46 titles for. 58 topographic, scales of. 14-15 Mathematical signs, forms and names of. 94 Measures, linear, metric equivalents of. 92 Measuring scales for map projection, use of. 44 Meridians used on public-land maps, diagram showing. 16 Metric measures, English equivalents of. 92 Millionth-scale map, use of. 14 Mine plans, conventional lines for. 29 features of. 65-66 symbols used on, plate showing. 20 Minerals. _See_ Rocks. Mississippi River Commission, maps published by 15 N. Names of rocks. 94-97 National forest maps and proclamations, use of. 15 O. Offset process, description of. 87 Oilwells, symbols for. 21 Opaquing, meaning of. 18, 47, 86 Orientation of maps, requirements for. 18 Original drawings, general treatment of, by draftsmen. 42-43 preparation of. 12-40 Outdoor sketches, redrawing of. 69-70 P.