GEOLOGICAL FIELD MAPPING 47 A pocket stereoscope is important if mapping involves the field use of air photographs A stereographic projection net assists in understanding structural relationships Binoculars allow the study of inaccessible rock faces and can help in locating exposures and routes A camera, preferably with the ability to take closeup as well as distant shots A penknife for conducting scratch tests, amongst other uses Sampling bags Field Clothing Clothing appropriate to the conditions allows the geologist to work comfortably throughout the day and not to be stressed by heat, cold, or wetness to the point at which concentration lapses and safety is at risk Typically, a day rucksack is carried, large enough to take spare clothing, food, water, mapping equipment, safety items, reference literature, and collected specimens In cold wet climates, the aim is to be warm and weatherproof by wearing items such as an undervest, shirt, fleece or sweater, and waterproof hooded anorak, plus a warm hat, scarf, and gloves Trousers are best made of quick-drying, close-weave cotton, not jeans, with further protection from waterproof overtrousers Well-cleated strong leather boots giving firm ankle support are recommended for most fieldwork, with wellington boots for wading activities Duvet clothing, warm padded footwear, and windproof outer garments are used in very cold dry climates In hot dry conditions, protection against direct sun radiation is best given by a loose, long-sleeved cotton shirt, long trousers, and a wide-brimmed sun hat, but short trousers and sleeves are preferred by many Corresponding footwear is lightweight whilst still providing support and grip Health and Safety A doctor can advise on what inoculations, vaccinations, and other medical precautions are needed for work in different parts of the world A first-aid kit should always be part of the field geologist’s equipment Items which come under the general heading of safety include goggles, a hard hat, torch, whistle, phone/radio, and survival bag Brightly coloured field clothing will help a search party, should the need arise Mapping Preliminaries Preparatory work before entering the field enables the survey to be conducted more efficiently Administrative aspects include obtaining permits, establishing how to contact medical and emergency services, and arranging that others know your daily whereabouts Relevant literature, maps, and borehole records will indicate what is known about the rocks and the nature of uncertainties Air photograph interpretation and the production of a photogeological map will identify the type of terrain, the range of solid and superficial units, and the principal structures One or more days will be needed for reconnaissance before mapping starts to provide first-hand knowledge of the rock types, mappable formations, nature of exposure, and style of structures Notes are made on access routes, areas of good and poor exposure, and parts that are inaccessible or hazardous An important act is to make contact with local people to explain the work and confirm permission Following the field visit, decisions can be made on mapping methods Often the most productive traverses are along streams which flow across the general strike and have cut down to bedrock Parts of an area may be best mapped by tracing the outcrop of a marker unit Broad area reconnaissance may dictate widely spaced traverses on parallel compass lines, whereas a mineral prospect might need enlarged scale mapping controlled by plane-tabling or compass and tape Measured stratigraphical sections and key structural areas can be drawn at large scale in the notebook The overall aim is to measure and record as many exposures as possible to cover the area within the allotted time, constantly remembering that the map and notebook must be easily read, understood, and followed by another geologist Hence exposures must be precisely located, symbols drawn neatly and accurately in conventional forms, numbers legible, and notes comprehensible Map and notebook must both distinguish between observation and inference Various symbols, colours, and abbreviations will be used to depict the geology Prepare a ‘key’ on the map to explain these, with formations in stratigraphical order Symbols There is no universal set of mapping symbols, but published lists have broad similarity and an example set is given in Figure Planar structures are generally depicted by a bar in the strike direction and a tick or other shape in the dip direction Linear structures are shown as arrows, with various head, shaft, and tail ornament Orientation measurements for lineations are given as an inclination angle (plunge) and its bearing (plunge direction) in the form 20/232 Two methods are in use for the orientation of planes One