Geoscience Reference
In-Depth Information
•
how weathered the rocks are;
Table 3.2
Possible places to
search for exposures. In the case of
animal burrows and where trees
have been disturbed the subsoil
type and small pieces of rock may
give an indication of the underlying
unit. This type of information should
be directly compared with similar
data collected from where the rocks
are exposed.
•
whether they are suitable for sampling without the need to
clean the exposures;
•
accessibility;
•
safety.
3
3.1.3 Locating your position
Geological data are spatial therefore it is very important to be
able to record the position of geological features accurately.
The fi rst part of this is locating the position of the exposure. If
you are using a GPS check that it is correctly adjusted for the
country that you are visiting or an appropriate grid system
(Section 2.4). Your position might also be immediately obvious
from a topographical map. There are instances, however, when
it is not possible to use either of these methods or when a more
accurate position is required. In this case use your compass for
triangulation (Section 2.3.3, Figures 2.11 and 2.12, pp.
22-24).
Potential exposure sites
Natural exposures in upland,
semi-arid and arid areas
All river and stream sections,
especially where there is a gradient
Foreshore and sea-cliffs
Mine and quarry workings
Footings of construction sites
Other methods of determining your position
In wooded areas, remote featureless regions and in some river
valleys it may not be possible to work out your position using
compass readings. Near to the Earth's poles compasses are
unreliable and you need to use a GPS or one of the shadow
stick methods (see Wiseman 1993). If you are in an area of
reasonably steep terrain an altimeter may help. In wooded
regions and other featureless places you can set a bearing on
your compass and walk along it. As you follow the bearing you
can count your paces either manually or using a pedometer and
hence calculate the distance that you have travelled from a
known point. For this you need to calibrate the length of your
normal paces by counting the number of paces you take over a
known distance. The distance you have travelled along
particular compass readings can be combined to produce
transects or traverses (Section 10.5.1).
Animal burrows
Uprooted tree bases
Road cuts
Tunnels
Back walls of landslides
Lakeside cliffs
When counting paces if you
count the times that you put
down just one of your feet
this will halve the chance of
making a mistake arising
from miscounting. If you have
lots of pacing to do it might
be worthwhile using a
pedometer.
3.2 Scale of observation, where to start
and basic measurements
Geological observations need to be made at a range of scales.
Start at the large regional scale: this will provide the overall
context. Then, consider the whole exposure, followed by units
within the exposure and fi nally focus down to the hand-
specimen scale.
3.2.1 Regional context
Before starting any fi eldwork it is essential to research the
regional setting, context and previous work. Aside from topics,
