The Project Gutenberg EBook of The Preparation of Illustrations for Reports of the United States Geologi, by John L. Ridgway This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org/license Title: The Preparation of Illustrations for Reports of the United States Geological Survey With Brief Descriptions of Processes of Reproduction Author: John L. Ridgway Release Date: July 16, 2013 [EBook #43232] Language: English Character set encoding: UTF-8 *** START OF THIS PROJECT GUTENBERG EBOOK THE PREPARATION OF ILLUSTRATIONS *** Produced by Tom Cosmas from materials scanned in and obtained from The Internet Archive. cover DEPARTMENT OF THE INTERIOR. JOHN BARTON PAYNE, Secretary United States Geological Survey GEORGE OTIS SMITH, Director [1] THE PREPARATION OF ILLUSTRATIONS FOR REPORTS OF THE UNITED STATES GEOLOGICAL SURVEY WITH BRIEF DESCRIPTIONS OF PROCESSES OF REPRODUCTION BY JOHN L. RIDGWAY U.S. Geol. Surv. WASHINGTON GOVERNMENT PRINTING OFFICE 1920 [2] THE PREPARATION OF ILLUSTRATIONS FOR REPORTS OF THE UNITED STATES GEOLOGICAL SURVEY BY JOHN L. RIDGWAY CONTENTS. Page. Part I. Preparation by Authors. Introduction 7 Purpose and value of illustrations 8 Selection and approval of illustrations 8 Submittal of illustrations 10 Kinds of illustrations 10 Sizes of illustrations 11 Subdivisions of plates and figures 12 Preparation of copy by authors 12 Character of original material 12 Preliminary preparation of maps 13 Material available for base maps 14 Basic features of maps 17 Standard scales 18 Orientation of maps 18 Projection 18 Explanation 19 Titles of maps and other illustrations 19 Symbols used on maps 20 General features 20 Letter symbols 20 Oil and gas symbols 21 Symbols for use on maps showing features of ground water 21 Black-line conventions 23 Materials used in preparing maps 23 Paper 23 Bristol board 24 Tracing linen 24 Inks 25 Drawing pens 25 Pencils 25 Rubber erasers and cleaners 25 Colored pencils and crayons 26 Water colors 26 Japanese transparent water colors 26 Coloring geologic maps 27 Diagrams 28 Essential features 28 Plans of mine workings 29 Sections 29 Lithologic symbols 32 [3] Use of photographs as illustrations 32 Essential features 32 Copyrighted photographs 33 Sources of photographs 34 Lending original photographs and drawings 34 Unpublished photographs 34 Specimens 34 General requirements 34 Borrowed and fragile specimens 35 Transmittal of paleontologic specimens 35 Making up plates 36 Reuse of illustrations 37 Approval of finished illustrations 38 Revision of illustrations 38 Submittal of proofs 38 Proof-reading illustrations 39 General considerations 39 Part II. Preparation by Draftsmen. General directions 41 Instruments 42 Classification of material 42 Preparation of maps 43 Projection 43 Details of base maps 45 Transferring or copying 46 Tracing 46 Celluloid transferring 47 Sketching by reticulation 47 The "shadowless drafting table" 47 Topographic features 48 Relief 48 Hydrography 51 Cultural features 52 Lettering 53 General directions 53 Lettering by type 54 Abbreviations 55 Names of railroads 57 Make-up of maps 57 Forms for certain features 57 Border 57 Title 58 Explanation 58 Graphic scales for maps 59 Symbols 61 Areal patterns for black and white maps 61 Standard colors for geologic maps 63 Reduction or enlargement of maps 63 Diagrams 64 Sections 64 Plans and cross sections of mines 65 Drawings of specimens of rocks and fossils 66 Methods used 66 Brush and pencil drawings 66 Pen drawings 67 Retouching photographs of specimens 68 Landscape drawings from poor photographs 68 Pen drawings made over photographs 68 [4] [5] Brush drawings from poor photographs 69 Outdoor sketches 69 Drawings of crystals 70 Retouching photographs 70 Part III. Processes of Reproducing Illustrations. Methods employed 72 Photoengraving 72 General features 72 Zinc etching 73 Copper etching in relief 75 Half-tone engraving 75 Three-color half-tone process 78 Wax engraving (the cerotype process) 80 Wood engraving 81 Photogelatin processes 82 Lithography 83 Original process 83 Photolithography 86 Offset printing 87 Chromolithography 87 Engraving on stone and on copper 89 Appendix. Length of degrees of latitude and longitude 91 Metric system and equivalents 92 Geologic eras, periods, systems, epochs, and series 92 Chemical elements and symbols 93 Greek alphabet 93 Roman numerals 93 Mathematical signs 94 Names of rocks 94 ILLUSTRATIONS. Page. Plate I.Methods of inserting plates and figures 10 II.Symbols used on geologic maps, economic maps, and mine plans 20 III.Lithologic symbols used in structure and columnar sections to represent different kinds of rock 32 IV.Symbols used on base maps 52 V.Reduction sheet used in lettering illustrations 54 VI.Half-tone prints showing effects produced by the use of six standard screens 56 VII.Details of the make-up of a geologic map 58 VIII.Patterns used to show distinctions between areas on black and white maps 60 IX.Diagrams and curves 64 Figure 1.Diagrams showing principal, guide, and auxiliary meridians, standard and special parallels and correction lines, and system of numbering townships, ranges, and sections 16 2.Conventional lines used in preparing plans and diagrams of mine workings to distinguish different levels 29 3.Section and perspective view showing relations of surface features to the different kinds of rocks and the structure of the beds 30 4.Sections of coal beds 31 5.Diagram illustrating method of projecting a map 44 6.Methods of expressing relief by contour lines, by hachures, by shading on stipple board, and by a brush drawing 49 [6] 7.Designs for bar scales 60 8.Method of making a bar scale for a map of unknown scale 60 9.Map bearing six areal line patterns 62 10.Diagram showing method of marking maps for reduction or enlargement (for record) 64 11.Structure section showing method of determining the succession of folds 65 THE PREPARATION OF ILLUSTRATIONS FOR REPORTS OF THE United STATES GEOLOGICAL SURVEY. By John L. Ridgway. Part I. Preparation By Authors. INTRODUCTION. There has been an obvious need in the Geological Survey of a paper devoted wholly to illustrations. No complete paper on the character, use, and mode of preparation of illustrations has been published by the Survey, though brief suggestions concerning certain features of their use have been printed in connection with other suggestions pertaining to publications. The present paper includes matter which it is hoped will be of service to authors in their work of making up original drafts of illustrations and to draftsmen who are using these originals in preparing more finished drawings, but it is not a technical treatise on drafting. The effectiveness of illustrations does not depend entirely on good drawings nor on good reproduction; it may be due in large part to the inherent character of the rough material submitted. If this material is effective or striking the finished illustrations, if well made, will be equally effective and striking. Each step in the making of an illustration—first the preparation of the author's original or rough draft, next the final drawing, and last the reproduction—is closely related to the others, and each is dependent on the others for good results. If the material has been well handled at all three steps the resulting illustration should be above criticism; if it has been poorly handled at any one of the three the effectiveness of the illustration is either impaired or ruined. A consideration of processes of reproduction is essential in the preparation of all illustrations, and the influence or effect of the process to be selected on the methods of preparing a drawing has seemed to warrant the presentation of brief descriptions of the processes usually employed by the Geological Survey. These descriptions include statements as to the kind of copy that is suitable for each process, the result produced by each, and the relative cost of the processes. PURPOSE AND VALUE OF ILLUSTRATIONS. An illustration in a report of the Geological Survey is not merely a picture having a remote bearing on the subject matter of the report; it must represent or explain something discussed or mentioned in order to become an illustration in the true sense of the term. The illustrations used in the Survey's reports are not employed for embellishment; the more pictorial kinds may be in some measure decorative, but decoration is distinctly not their primary purpose. The illustrations used in popular literature are designed to meet a public demand for ornament or attractiveness. Those used in scientific publications should be made plain and direct, without attempt to ornament or beautify. In the literature of science illustrations made by the reproduction of photographs or of explanatory diagrams or maps are intended simply to furnish greater illumination, and if the illustrations display photographic reality most statements or conclusions thus illuminated seem less open to dispute. A photograph may thus serve the double purpose of explanation and corroboration. The graphic expression of data and of details in a Survey report is intended to aid the reader in comprehending the report, and this is the prime advantage of its use, but it also enables the writer to omit from his text numerous descriptive details. It would generally be difficult without illustrations to present a clear picture of the geology [7] [8] of a region in its exact relations, and especially to describe adequately the form and the details of the structure of many fossils. The tasks of both the writer and the reader of reports on geology and kindred subjects are thus greatly facilitated by geologic maps, sections, paleontologic drawings, and illustrations of other kinds. The responsibility for good and effective illustrations rests largely upon the author, who should select and plan his illustrations with a view to their utility in aiding the reader to understand his report. SELECTION AND APPROVAL OF ILLUSTRATIONS. There is no rule limiting the number of illustrations that may be used in a publication of the Geological Survey, but in selecting illustrations for a report an author may easily fall into the error of over-illustration. The number of diagrammatic drawings or of drawings that express the author's deductions is rarely in excess of the needs of a paper, but the number of photographs submitted is often excessive. The number of pages in a manuscript may be a factor in determining the proper number of illustrations, but as the need of illustrations varies greatly from paper to paper this factor alone is not decisive. The tendency to overillustrate led the Director to issue the following order[1] governing the approval of illustrations: From Survey Order 63, Oct. 20, 1915. The primary responsibility for the selection of illustrative material shall rest upon the author and the chief of the branch transmitting the report: No one knows the subject matter of the report better than its author, though a sympathetic critic is usually needed to correct the personal equation that may express itself In an excessive number of illustrations or the use of photographs into which no one but the field man himself can read what he wishes to illustrate. The approval by the chief of branch of the illustrations selected by the author will be taken as vouching for those illustrations as essential and adequate, and the scientific value of the illustrations will not be subject to review in the section of illustrations. The chief of the section of illustrations shall decide the technical questions relating to the preparation of these illustrations for reproduction and may recommend the rejection of any that do not promise effective or economical reproduction. In the consideration of such questions, especially any relating to maps, the cooperation of the editor of geologic maps and chief engraver will be expected. The judgment of an author as to the illustrative value of a photograph is likely to be biased by his knowledge of the features that are actually included in the view represented, not all of which may be shown clearly in the photograph; his knowledge of all the features enables him to see more in his picture than his readers will be able to recognize without detailed description. Photographs in which special or significant features are obscured by foliage or lost in hazy distance do not make acceptable illustrations, and the use of a picture that requires much description to make it illustrate reverses, in a measure, the relations of text and illustrations. A photograph is not necessarily good for reproduction simply because it shows some particular feature to be illustrated; the quality of the print it will afford when reproduced from an engraved plate should also be considered. Some loss of detail by reproduction must be expected, and therefore only the clearest and most effective prints obtainable should be submitted. If an author has difficulty in making his preliminary or "original" drawings he may request that a draftsman be detailed to aid him. The request should be made to the Director through the chief of branch and properly approved. The work will then be done in the section of illustrations as advance preparation, but finished drawings should not be thus prepared unless the conditions are unusual. The administrative geologist reviews all illustrations submitted and represents the Director in matters relating to illustrations. SUBMITTAL OF ILLUSTRATIONS. All material intended for illustrations, except paleontologic specimens, should be submitted with the manuscript of the paper to be illustrated but in a separate package marked "Illustrations to accompany a paper on —— by ——." The package should contain a carbon copy of the list of illustrations that accompanies the manuscript or, if the titles to be printed on or with the illustrations include fuller descriptions than are given in that list, a carbon copy of the list giving complete titles and descriptions, the original of which should also accompany the manuscript. In the list each plate and figure should be separately numbered consecutively in the order in which it should appear in the report, and a figure opposite each title should show the number of the manuscript page on which the illustration is first mentioned or most fully discussed. Roman numerals should be used for the plates and arabic numerals for the figures. Each drawing or photograph should bear, in addition to the number and title, any suggestions concerning preparation, reduction, and method of reproduction which the author may consider especially desirable. The list should be headed "Illustrations." [9] [1] [10] U. S. GEOLOGICAL SURVEY PREPARATION OF ILLUSTRATIONS PLATE I Specimens other than fossils that are to be illustrated must be submitted directly to the section of illustrations, but the author may first obtain photographic prints of them in order to make up his plates. The specimens should be carefully packed and any that are fragile should be so marked. KINDS OF ILLUSTRATIONS. The illustrations in reports of the Geological Survey may be classified into five more or less distinct groups—(1) maps, (2) diagrams (including graphs, sections, plans, figures of apparatus, and stereograms), (3) outdoor photographs, (4) photographs and drawings of specimens, and (5) sketches. These may be further divided into two large groups, which may be called permanent and ephemeral. The permanent group includes illustrations that do not lose value through lapse of time or by natural alteration, such as detailed geologic maps, well-prepared structure sections, views of specimens, and good photographs or drawings of natural phenomena; the ephemeral group includes maps showing progress, key maps, diagrams showing yearly production, and many others that should be prepared in such a way as to minimize cost of preparation and reproduction. METHODS OF INSERTING PLATES AND FIGURES. 1, 2, 3, 5, 6, 7, plates; 4, 8, 9, 10, figures; 11, pocket. The illustrations will be finally divided into plates and figures when they are fully prepared, but if an author desires to determine the classification in advance of transmittal he should submit his material to the section of illustrations, where methods, processes, and reductions will be decided for each. In determining which shall be plates and which shall be figures, size and method of reproduction are the only factors to be considered; there are no other real differences. Illustrations that require separate or special printing, such as those reproduced by Lithography and by the photogravure, photogelatin, and three-color processes, must be printed separately from the text as plates and inserted in the report at the proper places; those that are reproduced by relief processes, such as zinc and copper etching and wax engraving, if not too large, can be printed with the text as figures. If an illustration to be reproduced by a relief process is marked for reduction to a size not exceeding that of the page of the text, it can be called a figure and be printed with the text. Half tones, though etched in relief, are rarely made text figures in Survey reports, because to give satisfactory impressions they must be printed on the best quality of coated paper, which is not used for the text. By using the coarser screens shown in Plate VI (p. 56), however, a half-tone cut may be made that can be used in the text if it is smaller than the page. SIZES OF ILLUSTRATIONS. The regular book publications of the Geological Survey are issued in three sizes—(1) octavo (annual reports of the Director, statistical reports on mineral resources, bulletins, and water-supply papers); (2) quarto (professional papers and monographs); (3) folio (geologic folios). The following table gives the measure of the text of each size and the measure of the trimmed page, in inches: Size of text. Size of page. Octavo 4 / by 7 / 5 / by 9 / Quarto 6 / by 9 / 9 / by 11 / Folio 13 / by17 / 18 / by 21 / Most professional papers are printed in two columns of type, each 3 inches wide, and folios are printed in three columns, each 4 / inches wide. A text figure in one of these publications can be made to fit one or more columns, and it may run the full length of the text page. The limits of the dimensions of plates and figures, in inches, are given in the following table. If for any reason a plate can not be reduced to the dimensions of a page it can be folded once or more; and if it is large and unwieldy it may be [11] 38 1516 78 18 116 18 14 58 1316 78 12 34 38 placed in a pocket on the inside of the back cover. (See Pl. I.) Single-page plate. Plate with one side fold. Text figure. Octavo 4 / by 7 / 7 / by 8 / 4 / by 7 / Quarto 6 by 9 9 / by 14 / 3 or 6 by 8 / Folio 15 by 17 / . . . . . . . . . . . . 4 / or 13 / by17 / For an octavo report a single-page plate with side title should be 4 inches or less in width, and a plate with bottom title should be 7 inches or less in depth. In other words, the actual depth and width of a single-page plate in a page of any size must depend on the number of lines in its title, the inclusion of which should not extend the matter much, if any, beyond the dimensions given in the table. A difference of 1 inch or less in the width of a folding plate may determine whether it must be folded once or twice, so that by consulting this table an author may save expense in binding and promote the reader's convenience in handling the plate. A text figure (including the title) can not extend beyond the text measure but may be of any size or shape within that measure, as shown on Plate I, figures 4, 8, 9, 10. SUBDIVISIONS OF PLATES AND FIGURES. If a plate consists of two or more parts or photographs each part should be marked with an italic capital letter—A, B, etc.—which should be placed directly under each. If it is made up of many parts, in the form of plates that accompany reports on paleontology, each part should be similarly marked with an arable numeral—1, 2, 3, etc. If a text figure is subdivided into two or more parts, each part should be marked with a roman capital—A, B, C, etc.; and if details of a part are to be described each detail should be marked by an italic lower-case letter—a, 6, c, etc. PREPARATION OF COPY BY AUTHORS. CHARACTER OF ORIGINAL MATERIAL. In the Geological Survey, as elsewhere, the "originals"—that is, the original material submitted by authors for the illustration of their reports—differ greatly in character and in degree of clearness. Some are carefully prepared; others are rough, obscure in part, and defective in detail. Drawings made from poor originals progress slowly, because the draftsman spends much time in interpreting uncertain features or in conference with the author concerning details. An original should be perfectly clear in detail and meaning, so that the draftsman can follow it without doubt. It should not consist of parts that must be brought together to make a new drawing, because the result of the combination of the parts will be uncertain at the outset and may not prove satisfactory. Each original illustration should be prepared with the idea that the draftsman who will make the finished drawing will be unfamiliar with the subject and will need definite instructions; all data should be plotted and each figure or plate should be completely made up before it is submitted. More or less roughly prepared originals are expected, but they should show no uncertainty in details. Obscure features may be cleared up by inclosing the features in penciled loops connected by a line with notes written on the margin, such as "omit this line," "turn at an angle of 30° from true north," "add," "cut out." PRELIMINARY PREPARATION OF MAPS. The base map that generally accompanies a report may be an original field sheet or it may have been compiled from various sources by an author and made to incorporate the results of his field work. It should not be a collection of maps of different scales and standards to be worked into a new map. The source of the data shown on every original base map should be indicated on the map, whether it is to be used as an illustration or as a record of field work. This information is required as a permanent record for showing the reliability of the map, for use in comparing data, and for giving full credit to those who are responsible for the data. An author should see that this requirement is observed in order that proper credit may be given and should especially see that all cooperative agreements and organizations are properly mentioned. An original map should preferably be complete in itself. It should not consist of several parts or sheets unless the data to be represented are unusually complex. All elaborate or technical finish of border lines, lettering, or like features should be left to the draftsman or the engraver. Base maps that involve the compilation of new data should be prepared by either the topographic branch or the division of Alaskan mineral resources. If a base map already published is to be reused it should be submitted to the chief topographic engineer or to the chief of the division of Alaskan mineral resources for approval. This procedure will insure a single standard of geographic accuracy in maps appearing in Survey publications. 38 12 12 12 38 12 12 34 12 12 38 1316 78 [12] [13] A geologist who requires a base map that includes new topographic data should address a request for its preparation to the chief geologist, who, through the Director, will refer the request to the topographic branch. The request must be accompanied by a full statement regarding the proposed report and the time when it is likely to be submitted. The preparation of such base maps by draftsmen in the division of geology, the land-classification board, the water-resources branch, or the section of illustrations has been discontinued except for the minor adaptations provided for above. If a report requires the preparation of a base map that includes no new topographic data such a map must be compiled from other authentic maps by the division or branch in which the report originates. If, however, no draftsmen are available in that division or branch, an arrangement can be made with any other branch—as the topographic or publication branch—that may have draftsmen available, with the understanding that the cost of the work shall be reimbursed to the branch doing the work by the branch ordering it. For indicating geologic and other data, however, an author may make use of an authentic base map already published, and after it is reduced or enlarged to appropriate scale by photography such a map may suffice for transmittal with a manuscript. MATERIAL AVAILABLE FOR BASE MAPS. The maps already published by the Geological Survey[2] and other Government bureaus should always be consulted when a new base is to be compiled. The following list includes most of the maps available: 1. The Survey's regular topographic atlas sheets, published on three scales—15-minute sheets, scale, 1:62,500; 30- minute sheets, scale, 1:125,000; 60-minute sheets, scale, 1:250,000—approximately 1 mile, 2 miles, and 4 miles to 1 inch, respectively—and its "special" maps,[2] some of which are published on other scales. All these maps can be used as bases for detailed geologic maps, for compiling maps on smaller scales, and for revising other maps. 2. The United States part of the international map of the world, now being published on the scale of 1:1,000,000 (approximately 16 miles to 1 inch). Each sheet of this map represents an area measuring 6° of longitude and 4° of latitude. The published sheets of this map may be used as bases for general maps. The sheets are drawn on the scale of 1:500,000, and photolithographs on this scale are available for use as bases for geologic or other maps. The adaptability of the 1:1,000,000 scale map to use as a base for general geologic maps is shown in the geologic maps of the southern peninsula of Michigan and of Indiana in Monograph 53 (Pls. IV and VII), the map of Florida in Bulletin 60 (Pl. I), and the map of Vermont in Water-Supply Paper 424 (Pl. I). 3. The Survey's two-sheet wall map of the United States, 49 by 76 inches, scale 1:2,500,000 (approximately 40 miles to 1 inch). Parts of this map can be used as bases for general geologic or other maps and as copy for index and other small diagrammatic maps. This map is published both with and without contours. 4. Land Office maps and township plats. These maps are now being published on a scale of 12 miles to 1 inch; they are also photo-lithographed on one-half that scale, or 24 miles to 1 inch. The township plats are printed on a scale of one-half mile to 1 inch. The maps are especially useful in compiling maps in which land lines (townships and sections) are essential, and the township plats afford valuable detail and are useful in field work and in revising other maps. Township and section lines should appear on all land-classification maps published by the Survey. On maps on a scale less than 1:250,000 only the townships should be shown; on maps on scales greater than 1:250,000 the sections should be shown; on maps on a scale of 1:250,000 the sections should be shown, unless their representation will materially impair the legibility of the map, in which case only the townships should be shown. (See fig. 1.) 5. Post-route maps, covering single States or groups of adjacent States, published on sheets of different sizes and on scales determined mainly by the size of the State. The map of Texas is published on a scale of 12 miles to 1 inch, that of Virginia on a scale of 7 miles to 1 inch, and that of West Virginia on a scale of 6 miles to 1 inch. Both the Land Office and the post-route maps are useful for reference in compiling maps on smaller scales. Post-route maps are especially useful for comparing and verifying the location of cities, towns, and railroads. 6. Coast and Geodetic Survey charts, published on scales that are governed by the area represented and the amount of detail to be shown. These maps should always be used in compiling and correcting coast lines. 7. Maps and charts published by the Corps of Engineers of the Army, the Mississippi River Commission, the surveys of the Great Lakes, and the boundary surveys. These maps are especially useful if the scale of the map to be compiled requires considerable detail. 8. The Survey's three small base maps of the United States—(a) a map 18 by 28 inches, scale 110 miles to 1 inch, which is published both with and without contours, or with relief or hypsometric shading; (b) a map 11 by 16 inches, scale 190 miles to 1 inch; (c) a map 7 / by 12 inches, scale 260 miles to 1 inch, designed for use as a two-page illustration in a bulletin or a water-supply paper. 9. The Century, Rand McNally & Co.'s, Cram's, Stieler's, The Times, Johnston's Royal, and county atlases. 10. State and county maps. [14] [15] 12 11. Railroad surveys, which are useful in furnishing data for elevations as well as for locations of towns and stations. 12. The latest national-forest maps and proclamations. It is, however, not necessary that national forests, bird reservations, and national monuments be shown on a map in a report unless their addition is specially requested by the author or by the chief of the branch submitting the report, and they should not be shown if they will obscure other more important data. See "Topographic maps and folios and geologic folios published by the United States Geological Survey" (latest edition). Figure 1.—Diagrams showing principal, guide, and auxiliary meridians, standard and special parallels and correction lines, and system of numbering townships, ranges, and sections. The Survey has published numerous maps of parts of Alaska, as well as other maps, which are available for use or reuse in its reports. Copies of all base maps for which copper plates have been engraved by the Survey can be obtained on requisition, and their use in a new report will save time as well as the cost of engraving. Other maps will be found in the Survey library, where the latest editions only should be consulted. BASIC FEATURES OF MAPS. It must be remembered that "every map, whatever its scale, is a reduction from nature and consequently must be more or less generalized."[3] The degree of generalization in the geologic and other detail to be shown on a map usually involves a corresponding degree of generalization in its base. Absolutely true generalization means the same degree of omission of detail for each kind of feature. If a base map on a scale of 1 mile to 1 inch, prepared with the usual detail, were placed before a camera and reduced to a scale of 16 miles to 1 inch, the lines representing the smaller tributaries of streams and the smaller water bodies, as well as many other features, would probably be so greatly reduced in length as to be illegible. If from this reduced photograph a new map were prepared, from which all features not plainly discernible were omitted, the new map should represent what might be called true generalization. This degree of generalization is, however, not practicable, but unessential detail should be systematically omitted. The amount of detail which a base map should show is limited by its scale, by the character of the country it represents, and by the kind of data to be shown. Coordinate features of a topographic map should be shown with equal detail. Detail in culture may call for detail in drainage, though relief may be greatly generalized or entirely omitted; detail in relief may like-wise call for detail in drainage, though culture may be more generalized. Gannett, Henry, A manual of topographic methods: U. S. Geol. Survey Mon. 22, p. 107, 1893. [2] [16] [17] [3] If the three fundamental features of a topographic map—the culture, the drainage, and the relief—are to be engraved or photo-lithographed separately and printed in colors, the best results can be obtained by drawing each feature in a separate color on one sheet unless the work is coarse and great precision in register is not needed. The culture should be drawn in black waterproof ink, the drainage in Prussian blue, and the relief in burnt sienna; but care should be taken that the colors used will photograph well. To insure a good photograph it is usually necessary to add a little black to the blue and brown. (See "Inks," p. 25.) The photographer will then make three negatives and will opaque or paint out all but one of the three features on each negative. The cost is somewhat greater than that of reproducing three separate drawings, but the result gives more accurate register than if the drawings were made on separate sheets, which are likely to change in size before they are reproduced. STANDARD SCALES. The standard scales of the maps used in the publications of the Geological Survey are fractions or multiples of 1:1,000,000 (see p. 14), except for a map that is reduced expressly to fit one or two pages of a report or that is reduced horizontally or vertically to fit the text as a small diagrammatic or index map. It should be remembered that a map which may be serviceable for use in compiling a new map, except as to scale, can be reduced or enlarged to the scale of the new drawing by photography, by a pantograph, or by other means. (See p. 47.) Maps compiled by an author should be prepared on a scale of at least 1 / times and preferably twice the size of the scale used on the published map. Maps traced on linen should be no less than twice the size of publication. Not only is the quality of the reproduction improved by considerable reduction, but the larger scale of the drawing facilitates the plotting of details. It should be remembered, however, that a linear reduction of one-half produces a map only one- fourth the area of the original, and reduction so great may prevent the addition of data, such as an extended note in small letters applying to a small area on the face of a map, which would not be legible when reduced. ORIENTATION OF MAPS. A map that bears no arrow indicating north is supposed to be oriented north and south, and its title should read from west to east. If, however, the area mapped has a general trend in one direction, as northwest to southeast, and its squaring up by a north-south line would leave too much blank paper, this general rule is not followed. The border lines on such a map should conform to the general trend of the area mapped, an arrow should show north, and the title and scale should be placed horizontally, but the projection numbers and town names should follow the direction of the parallels of latitude. (See Pls. X and XII, Bull. 628; and Pls. VI, XV, and XVI, Mon. 52.) PROJECTION.[4] See also pp. 43-45, where the method of projecting a map is more fully explained. The polyconic projection has been adopted by the Geological Survey for its topographic atlas sheets and must be consistently used for its other maps. If a new map is to be compiled an accurate projection should first be constructed, and no plotting should be done on it until the projection has been checked and found to be correct. A projection should be checked or proved by some one other than the person who prepared it. Next the drainage and the water areas should be outlined; then the cultural features should be added; and finally the relief, whether expressed by contour lines, hachures, or shading.[5] See pp. 49-48 for methods of tracing and transferring. EXPLANATION. Under the heading "Explanation" should be placed all matter needed to describe fully the details of an illustration, whether map, diagram, or section, so that if the illustration became detached it would be a complete self-explanatory unit. The explanation of a map may be placed inside the border lines if there is ample room for it, or it may be placed outside. The standard arrangement for an outside explanation for geologic maps is shown, in the geologic folios, which should be followed in general form. If there is space within the border lines the explanation may be appropriately arranged therein, either in a vertical column or horizontally, according to the size and shape of the space available. If the sequence of formation is shown by horizontal arrangement the younger formations are placed at the left and the older at the right. If it is shown by a vertical arrangement the youngest formation is placed at the top. Each original map submitted by an author should have at least 4 / inches of blank margin on the right and at the bottom in which to place the explanation, scale, title, and other matter, but the author should make no attempt to elaborate these features nor should he employ a draftsman to letter them carefully. Plainly written ordinary script is quits sufficient for original maps; the final lettering, which may consist entirely of impressions from type, will be added after submittal of a report. [18] 12 [4] [19] [5] 12 TITLES OF MAPS AND OTHER ILLUSTRATIONS. The titles of maps should be supplied by authors but are subject to revision in order to make them agree with established forms. They should be written in ordinary script, not carefully lettered. They should state concisely the kind of map, the area shown, the special features represented, and the county, State, or Territory in which the area is located. (See p. 58.) Titles are reproduced directly only on lithographs, three-color prints, photogelatin plates, and other illustrations that are printed by contractors, not by the Government Printing Office. The titles of illustrations that are repro duced by relief processes, such as zinc etching, half tone, and wax engraving, are printed at the Government Printing Office from type, and proofs are submitted to the authors for examination. SYMBOLS USED ON MAPS. GENERAL FEATURES. More than 200 symbols have been used on maps to express 25 different kinds of data, a fact indicating at once a notable lack of uniformity and a need of standardization. It is of course impossible to provide a characteristic symbol that can be used uniformly for each kind of feature, and therefore the same symbol may be used on different maps to express different things. The symbols shown in Plate II are those most used on geologic maps. The symbols for dip and strike, fault lines, mine shafts, prospects, and several others are generally well known, but on some maps it may be necessary to modify a standard symbol to express additional distinctions. The symbols shown, however, will cover all the ordinary requirements of miscellaneous mapping. Though the plate shows more than one symbol for some features the symbol most commonly used is given first and should be preferred. The center of each symbol should mark the location of the feature symbolized. Symbols are not always platted with sufficient care. On small-scale maps they are difficult to locate and unless great care is taken in platting them they are likely to be several miles out of place. All symbols should be located precisely where they belong. The symbol showing dip and strike should be accurately platted by means of a protractor, so that the strike will be shown graphically, without a number and a degree mark, and not need replatting by a draftsman or engraver. The dip, however, should be indicated by a number and a degree mark. LETTER SYMBOLS. The letter symbols used on most geologic maps to indicate the ages and names of the formations represented consist of two or more letters—an initial capital letter for the name of the system and one or more lower-case letters for the name of the formation or of the material, as Qt (Quaternary—lower terrace deposits); Cpv (Carboniferous— Pottsville formation); COk (Cambrian-Ordovician—Knox dolomite), etc. The standard usage for this feature is shown in the geologic folios but is subject to modification in other publications. In preparing an original geologic map a letter symbol, such as has been just described, or a number should be put in the proper place in the explanation, and the same symbol or number should be repeated at one or more places on the map within the areas to which it refers. Each area that is indicated by a color should be marked with the proper symbol in order to make its identification sure, for light colors especially are likely to fade and mixed colors can not be discriminated with certainty. [20] U. S. GEOLOGICAL SURVEY PREPARATION OF ILLUSTRATIONS PLATE II SYMBOLS USED ON GEOLOGIC MAPS, ECONOMIC MAPS AND MINE PLANS OIL AND GAS SYMBOLS. A complete set of symbols for maps showing oil and gas is given on Plate II. Referring to these symbols the chief geologist, in a memorandum to the Director, writes: [21]