Geoscience Reference
In-Depth Information
geological fi eld sketch is a combination of a simple line
drawing of the relevant geological features you can observe and
your initial geological deductions. Thus photographs are not a
replacement for sketches because they are neither selective nor
deductive and you cannot add labels and cross references.
Professional geologists regularly use a combination of
photographs and sketches. Producing fi eld sketches is the
notebook skill that most students of geology and even some
professionals fi nd very diffi cult, but it is a skill that is well
worth developing.
4
Figure 4.3 (p. 60) shows a range of different types of sketch and
styles. They all record geological data. Simple two-dimensional
sketches can provide an effective summary of many different
features at a variety of scales (Figure 4.3a-d). In contrast,
three-dimensional sketches of sedimentary structures are
complex and diffi cult to execute (Figure 4.3e). In this case the
author has also bravely tried to show the shape of the
sandstone block the structure was preserved in. This type of
sketch is not generally recommended because: (1) it is hard to
draw and (2) the sedimentary structure is confused with the
shape of the weathered surfaces; (3) the shape of the block is
also irrelevant to the purpose of the exercise which was to
record the sedimentary structure. Simple sketch cross-sections
showing the topography, exposures and main geological units
(Figure 4.3d) are useful overviews. Where the relationships
between different rock units are complex a sketch will help to
focus observations (Figure 4.3f). Figure 4.3f also shows
effective use of colour and an inset box to show more detail
of one part.
4.3.1 General principles: Aims, space
and tools
Before you start sketching you should decide on the aims
of the sketch. One way to do this is to start by writing
down the title or caption of the sketch encapsulating the
aims. Sketches are usually drawn freehand in pencil (i.e.
not with a ruler). Drawing in pencil is advantageous because
it allows you to erase mistakes and/or redraw part of the
sketch. With a pencil it is also easier to draw lines of
different thickness and boldness as well as shading part
of the fi gure to bring out different features (Figure 4.4, p. 62).
A minority of people sketch directly in pen but this is not
recommended because it is impossible to correct mistakes
or make improvements, so the accuracy is compromised.
Most sketches look better on plain paper, although some
people fi nd that lined or graph paper is useful for scaling.
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