Chapter III: 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

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.