52 GEOLOGICAL FIELD MAPPING field evidence, such as a change in soil composition, soil colour, slope change, topographical feature, spring line, and change in vegetation, and recording these on the map Study of air photographs may help A boundary is pencilled on the map in a position which fits the evidence best, drawn as a full line if well constrained, or long or short dashes for decreasing confidence It is clear that geological field mapping means making a map in the field whilst the evidence is in sight, not placing locality numbers on the map to plot the data later and draw arbitrary lines between rock changes An example of field map entries is given in Figure At the end of the field day, the map and notebook are inked in to make a permanent record, using coloured ink on the map as appropriate (Figure 4) Ink the notebook drawings accurately to preserve the lines made whilst the object was in view Analyse structural data on a stereonet and construct trial cross-sections Never leave a field area without drawing at least one geological cross-section Specimens collected during the day are given permanent labels and laid out for further reference It is helpful at this stage to summarize the day’s findings, place it in context, and make notes for the final report Superficial Deposits Some areas are deeply weathered and covered by residual soils or regolith through which only the most resistant rocks emerge at the surface Others are blanketed by transported materials, such as windblown sands or glacial deposits For residual soils, information can be obtained by a study of auger samples, recording parameters such as soil colour, composition, and consistency Look also for fragments (‘float’) brought to the surface by fallen trees, ploughing, or burrowing animals Air photographs can prove to be useful in indicating boundaries, particularly where vegetation is well controlled by soil type and has been little disturbed by human activity For transported materials, the geologist aims to outline the deposit and classify the type The ‘drift’ maps of the BGS, for example, show various kinds of gravel, sand, and clay deposits formed from standing, moving, or melting ice, plus river terraces, fluvial and estuarine alluvium, peat, and others Some can be clearly seen and mapped from air photographs or a high vantage point Relevant observations are placed on the field map by a selection of colours, overprint symbols, and notes Areas of slope failure should be marked Ancient soils are not commonly preserved in the stratigraphical column but may have left traces, such as weathered and reddened surfaces; here, a knowledge of soil processes helps in assessing the palaeoclimate See Also Engineering Geology: Geological Maps; Natural and Anthropogenic Geohazards; Site and Ground Investigation; Ground Water Monitoring at Solid Waste Landfills Environmental Geology Geochemical Exploration Geological Maps and Their Interpretation Geological Surveys Geomorphology Remote Sensing: GIS Seismic Surveys Soil Mechanics Soils: Modern Further Reading Allum JAE (1966) Photogeology and Regional Mapping Oxford: Pergamon Barnes JW (1991) Basic Geological Mapping, 2nd edn Geological Society of London Handbook, Milton Key nes: Open University Press Boulter CA (1989) Four Dimensional Analysis of Geo logical Maps Chichester: Wiley Compton RR (1985) Geology in the Field New York: Wiley Lattman LH and Ray RG (1965) Aerial Photographs in Field Geology New York: Holt, Rinehart and Winston Lillesand TM and Kiefer RW (1979) Remote Sensing and Image Interpretation New York: Wiley Maltman A (1990) Geological Maps: An Introduction Milton Keynes: Open University Press McClay KR (1987) The Mapping of Geological Structures Geological Society of London Handbook Milton Key nes: Open University Press Moseley F (1981) Methods in Field Geology Oxford/San Francisco: Freeman Ramsay JG and Huber MI (1987) The Techniques of Modern Structural Geology, vol 2, Folds and Fractures London: Academic Press Ray RG (1960) Aerial Photographs in Geologic Interpret ation and Mapping United States Geological Survey Professional Paper 373 Washington: US Government Printing Office Tucker ME (1982) The Field Description of Sedimentary Rocks Geological Society of London Handbook Milton Keynes: Open University Press