Geological maps: An Introduction

A recent national survey of geology students indicated that, In a subject so fundamental and yet so varied, every although they saw the need for a basic training in map­ geologist will have his own views on geological maps - the work, the three-dimensional aspects involved formed the matters needing emphasis, the best methods of interpreta­ single most difficult part of an introductory geology tion, good examples of maps, and so on. Instructors may course, and that it was generally taught in a way both ab­ therefore urge in their taught courses different priorities stract and dull. At the same time, there was no book which from those given here, and, although a wide range of maps puzzled students could turn to for explanations; no book and map exercises is included, will prefer to continue to which told them more about real geological maps. This use their own 'pet' examples. But this is meant primarily to book is an attempt to fill that need. It is based on the view be a book for the student - to turn to for clarification, for that in these days of increasing specialisation the geological further information, and simply to learn a little more about map remains the vital coordinating document, and that the geological maps.

1 Some fundamentals of geological maps.- 1.1 Introduction.- 1.2 The topographic base map.- 1.2.1 Scale.- 1.2.2 Map projection.- 1.2.3 Grid systems and location.- 1.2.4 Relief.- 1.2.5 Key or legend.- 1.3 Geological aspects.- 1.3.1 Key or legend.- 1.3.2 Superficial and bedrock maps.- 1.3.3 The third dimension: geological cross-sections.- 1.3.4 The interpretive nature of maps.- 1.3.5 Aesthetics.- 1.4 Summary chapter.- 1.5 Selected further reading.- 2 The nature of geological maps: the Ten Mile map of the UK and the 1: 2 500 000 map of the USA.- 2.1 Introduction: cartographic matters.- 2.2 Interpretation of the maps: geology and relief.- 2.3 Map patterns and geological structure.- 2.3.1 Dipping formations.- 2.3.2 Unconformities.- 2.3.3 Folded rocks.- 2.3.4 Faulted rocks.- 2.3.5 Igneous rocks and geological histories.- 2.4 Conclusion.- 2.5 Summary of chapter.- 3 The three-dimensional aspect: structure contours.- 3.1 Introduction.- 3.2 The nature of structure contours.- 3.3 Examples of structure contours on maps.- 3.4 Structure contours derived from borehole/well information.- 3.5 Structure contours derived from topography: the theory.- 3.6 Structure contours derived from topography: the practice.- 3.7 Structure contours from topography and boreholes.- 3.8 Straight structure contours.- 3.9 Summary of chapter.- 3.10 Selected further reading.- 4 Measurements in three dimensions: strike and dip, formation thickness and depth.- 4.1 Introduction.- 4.2 Strike and dip.- 4.3 Apparent dip.- 4.4 Formation thickness.- 4.5 Formation depth.- 4.6 The ‘three-point’ method.- 4.7 Summary of chapter.- 4.8 Selected further reading.- 5 Geological cross-sections.- 5.1 Introduction.- 5.2 Line of section.- 5.3 Scale and vertical exaggeration.- 5.4 Manual drawing of cross-sections.- 5.5 Structure and stratigraphic sections.- 5.6 Three-dimensional diagrams.- 5.6.1 Fence diagrams.- 5.6.2 Block diagrams.- 5.7 Summary of chapter.- 5.8 Selected further reading.- 6 Visual assessment of outcrop patterns.- 6.1 Introduction.- 6.2 Horizontal formation.- 6.3 Dipping formations.- 6.3.1 Recognition.- 6.3.2 Assessment of formation dip in valleys.- 6.4 Vertical formations.- 6.5 Assessment of formation thickness.- 6.6 Summary of chapter.- 6.7 Exercises on visual assessment.- 7 Unconformities.- 7.1 Introduction.- 7.2 Terminology.- 7.3 Recognition on maps.- 7.4 Associated features.- 7.5 Use on maps.- 7.6 Palaeogeological maps.- 7.7 Summary of chapter.- 7.8 Selected further reading.- 8 Folds.- 8.1 Introduction.- 8.2 Description from maps.- 8.2.1 The parts of a fold.- 8.2.2 Fold orientation.- 8.2.3 Fold attitude.- 8.2.4 Fold shape.- 8.2.5 Fold style.- 8.2.6 Fold dimensions.- 8.3 Visual assessment on maps.- 8.4 Measurements on maps.- 8.5 Summary of chapter.- 9 Faults: the fundamentals.- 9.1 Introduction.- 9.2 Fault parts, orientation and dimensions.- 9.3 Fault displacement.- 9.4 Classification of faults.- 9.5 Visual assessment on maps.- 9.6 Measurements on maps.- 9.7 Summary of chapter.- 10 More on faults: contraction (thrust), extension, and strike-slip faults.- 10.1 Introduction.- 10.2 Contraction (thrust) faults.- 10.2.1 Characteristics.- 10.2.2 Recognition on maps.- 10.2.3 Three-dimensional arrangement.- 10.2.4 Displacement amount, direction and sequence.- 10.3 Extension faults.- 10.3.1 General.- 10.3.2 Characteristics.- 10.3.3 Extension faults on maps.- 10.4 Strike-slip faults.- 10.4.1 Characteristics.- 10.4.2 Recognition on maps.- 10.5 Summary of chapter.- 10.6 Selected further reading.- 11 Igneous and metamorphic rocks; mineral deposits.- 11.1 Introduction.- 11.2 Igneous rocks.- 11.2.1 Volcaniclastic rocks.- 11.2.2 Magmatic rocks.- 11.3 Metamorphic rocks.- 11.4 Mineral deposits.- 11.5 Summary of chapter.- 11.6 Selected further reading.- 12 Geological history from maps.- 12.1 Introduction.- 12.2 Sedimentary successions.- 12.3 Deformed rocks.- 12.4 Non-sedimentary rocks.- 12.5 Reading a geological map.- 12.6 Writing a map report.- 12.7 Summary of chapter.- 13 The production of geological maps.- 13.1 Introduction.- 13.2 The field survey.- 13.3 Preparation of maps for publication.- 13.3.1 Scale.- 13.3.2 Boundaries.- 13.3.3 Key and other information.- 13.3.4 Ornament.- 13.4.5 Colour.- 13.4 Map reports.- 13.5 Availability of maps.- 13.6 Conclusions.- 14 The heritage of geological maps.- 14.1 Introduction.- 14.2 A short history of geological maps.- 14.3 The contributions of some individuals.- 14.3.1 Jean Etienne Guettard (1715–86).- 14.3.2 William Smith (1769–1839).- 14.3.3 John MacCulloch (1773–1835).- 14.3.4 John Phillips (1800–74).- 14.3.5 John Wesley Powell (1834–1902).- 14.3.6 Sir Edward Bailey (1881–1965).- 15 Current trends in geological maps.- 15.1 Introduction.- 15.2 New technologies in geologicam mps.- 15.2.1 Field surveying.- 15.2.2 Remote sensing.- 15.2.3 Computer methods in map manipulation and production.- 15.2.4 Map storage, indexing and retrieval.- 15.3 New forms in geological maps.- 15.4 Specialised and thematic maps.- 15.5 Summary of chapter.- 15.6 Selected further reading.- References.