Geoscience Reference
In-Depth Information
the long edge at the same angle as the features whose dip
you are trying to estimate, read off the apparent dip.
•
Inset boxes for detail:
In some cases the geological feature
repeats itself on the small scale, or there is one particular
part of the cliff that you want to collect data on in more
detail. So rather than putting the detail in for the entire cliff
face one useful technique is to draw the main features on
the sketch and then add a box to indicate the area where a
photograph has been taken or a more detailed sketch has
been constructed (Figures 4.3f and 4.4, pp. 60 and 62). This
also enables you to draw the detailed part at a larger scale
if appropriate.
•
Colour:
A green coloured pencil can be useful for showing
the vegetation and clearly separates it from the geological
part of the sketch (Figure 4.4). A red or blue coloured
pencil is useful for cross references, particular items or key
features (Figures 4.2b and 4.3f, pp. 58 and 60).
4
4.3.2 Sketches of exposures
Sketches of whole, or representative parts of, exposures such as
sea-cliffs, road cuts and quarry faces are commonly used to
observe and show one or more of the following:
•
the main units and the geometric relationship(s) between
them;
•
large-scale (metres to tens of metres) structures such as
folds, faults and angular unconformities;
•
the position of more detailed measurements (e.g. samples or
a graphic log; see Section 6.3 and Chapter 13) so that the
exact location can be easily relocated.
In most instances it is best to take up an entire page, or even
two facing pages, of a hardcopy notebook when constructing a
sketch of a cliff or quarry face. Also consider the orientation of
the notebook; would the subject matter be best captured with
the notebook page orientated landscape (i.e. wider than it is
taller) or portrait (i.e. taller than it is wider)? Long cliff faces
are usually best landscape whereas a vertical profi le through a
cliff might be better portrait. Figure 4.5b-f (pp. 64-65) shows
how you might build up a sketch of the cliff shown as a
photograph in Figure 4.5a. While these instructions are divided
into suggested steps it may be necessary to amend the order
depending on the subject matter, or go back to a previous step
to add or amend the detail. The aim of the exercise in the case
of Figure 4.5 is to summarize the main rock units and the
relationship(s) between them.
For shading, a softer (HB or
less) conventional type of
pencil rather than a
mechanical pencil is better.
Hold the pencil so that the
side of the pencil lead is in
contact with the paper to
execute the shading. Varying
the amount of pressure results
in different depths of
shading. Gently rub the tip of
an index fi nger over the
shading in a circular motion
if you wish to smooth the
shading out further.
