I do not recall how I obtained this, but it is was authored by Mark Helper who is a
great field geologists at UT (we won't hold that against him) and who worked in the
Klamaths for his dissertation years ago. It's a nice review of aspects of using
Brunton complasses in the field.
Introduction to the Brunton Compass
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Geo420k, Lab 1
M. Helper, Jackson School of Geosciences, UT Austin
Parts of the Brunton Compass
Mirror
Lift Pin for
Needle
Needle
Compass
Card
Bull’s Eye
Level
Sighting Arm
Image from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
M. Helper, Jackson School of Geosciences, UT Austin
Clinometer
Level
Parts of the Compass Face
Note this is an
azimuthal compass,
as opposed to a
quadrant compass.
Image from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
M. Helper, Jackson School of Geosciences, UT Austin
Compass Mastery
• Locate North, Set local declination
• Measure Bearings
• Measure Strike and Dip of planes
• Measure Trend and Plunge of lines
• Measure Vertical Angles
o
measuring height / thickness of a feature
M. Helper, Jackson School of Geosciences, UT Austin
Recording a Bearing
Bearing: direction from one point to another
NO
Recording notation:
• Azimuth: “247°”
360
NW
W 270
NE
O
O
90 E
O
O
247
67
SE
O.
180
S
• Quadrant:“S 67°W”
M. Helper, Jackson School of Geosciences, UT Austin
Measuring Strike
Strike: Direction of the line of intersection between a
tilted plane and a horizontal plane
Aerial View: Strike of Dipping
Strata
Strike
Strike
(E.F. McBride)
Image from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
M. Helper, Jackson School of Geosciences, UT Austin
Measuring Strike
Measuring a field book that defines the tilted plane of interest
M. Helper, Jackson School of Geosciences, UT Austin
Measuring Strike
Strike: Direction of the line of intersection between a
tilted plane and a horizontal plane
Strike
Images from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
• Compass must be horizontal (bull’s eye bubble
centered), with compass edge flush to the tilted plane
M. Helper, Jackson School of Geosciences, UT Austin
Recording Strike
In the picture at left, is the strike 157o or 337o?
Right-hand Rule:
• Record the bearing in the
direction that places the
dip direction of the plane to
the right (clockwise from)
strike.
Answer: 337o
Strike
Strike
Images from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
M. Helper, Jackson School of Geosciences, UT Austin
Measuring Dip
Dip: The maximum slope of a plane, measured from
horizontal. The dip direction is always perpendicular to strike.
The dip direction is:
• The “fall line” in
skiing
• The direction water
runs down a
sloping surface
• The direction a
pebble rolls down a
sloping surface
W
Horizontal
Dip Angle
(E.F. McBride)
M. Helper, Jackson School of Geosciences, UT Austin
E
Measuring Dip
M. Helper, Jackson School of Geosciences, UT Austin
Measuring Dip
Images from:
http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
• Place compass on its
side, perpendicular to
strike
• Level the clinometer
(center the bubble)
• Read the dip, i.e. 36o
M. Helper, Jackson School of Geosciences, UT Austin
Recording Strike & Dip
Shorthand Notation:
337/36o
or
337/36o NE
• “NE” records the dip
direction, but is redundant
if the right-hand rule is
followed
Images from:
http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
M. Helper, Jackson School of Geosciences, UT Austin
Measuring the Trend of a Linear Feature
Trend: The orientation of a line, in the direction that
it is inclined.
1. Point the Sighting Arm
of compass parallel to
the direction the
feature plunges
2. Hold compass level
3. Read the white end of
the compass needle
Glacial Striations (Maine)
M. Helper, Jackson School of Geosciences, UT Austin
M. J. Cooke
Measuring the Plunge of a Linear Feature
1. Place the side of
the compass
parallel the
feature
2. Measure the
angle of the line
from horizontal
with the
clinometer, as
done for dip
Horizontal
Plunge
Glacial Striations (Maine)
M. Helper, Jackson School of Geosciences, UT Austin
M. J. Cooke
Recording Trend and Plunge of a Line
Shorthand Notation:
“25o/150”
Horizontal
Reads:
“plunges 25
degrees toward a
bearing of 150o”
Plunge = 25o
Trend = 150o
M. J. Cooke
M. Helper, Jackson School of Geosciences, UT Austin