The document introduces the parts and functions of the Brunton compass, which is used to measure orientations in the field. It describes how to measure strike and dip of tilted planes, bearings between locations, and trend and plunge of linear features. Key parts are the needle, clinometer, and sighting arm. Strike is measured by placing the compass flush on the tilted plane. Dip direction is read perpendicular to strike. Trend is measured parallel to the feature using the sighting arm. Plunge uses the clinometer. Examples are given for recording strike/dip, bearings, and trend/plunge.

1. M. Helper, Jackson School of Geosciences, UT Austin
Introduction to the Brunton Compass
Geo420k, Lab 1

2. M. Helper, Jackson School of Geosciences, UT Austin
Mirror
Lift Pin for
Needle
Compass
Card
Sighting Arm
Parts of the Brunton Compass
Needle
Bull’s Eye
Level
Clinometer
Level
Image from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm

3. M. Helper, Jackson School of Geosciences, UT Austin
Parts of the Compass Face
Image from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm

4. M. Helper, Jackson School of Geosciences, UT Austin
• 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
Compass Mastery

5. M. Helper, Jackson School of Geosciences, UT Austin
Recording a Bearing
Recording notation:
• Azimuth: “247°”
Bearing: direction from one point to another
S
W
N
NE
NW
SE
270
O
360
O
90
O
180
O.
247
O
E
67
O
• Quadrant:“S 67°W”

6. 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
(E.F. McBride)
Aerial View: Strike of Dipping
Strata
Strike
Strike
Image from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm

7. Measuring Strike
M. Helper, Jackson School of Geosciences, UT Austin
Measuring a field book that defines the tilted plane of interest

8. 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
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
Strike

9. M. Helper, Jackson School of Geosciences, UT Austin
Recording Strike
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
In the picture at left, is the strike 157o or 337o?
Images from: http://courses.geo.ucalgary.ca/glgy203/images/sd.htm
Strike
Strike

10. M. Helper, Jackson School of Geosciences, UT Austin
Measuring Dip
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
(E.F. McBride)
Horizontal
Dip Angle
W E
Dip: The maximum slope of a plane, measured from
horizontal. The dip direction is always perpendicular to strike.

11. Measuring Dip
M. Helper, Jackson School of Geosciences, UT Austin

12. M. Helper, Jackson School of Geosciences, UT Austin
Measuring Dip
• Place compass on its
side, perpendicular to
strike
• Level the clinometer
(center the bubble)
• Read the dip, i.e. 36o
Images from:
http://courses.geo.ucalgary.ca/glgy203/images/sd.htm

13. 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

14. M. Helper, Jackson School of Geosciences, UT Austin
Measuring the Trend of a Linear Feature
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
Trend: The orientation of a line, in the direction that
it is inclined.
Glacial Striations (Maine) M. J. Cooke

15. M. Helper, Jackson School of Geosciences, UT Austin
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
Measuring the Plunge of a Linear Feature
M. J. Cooke
Plunge
Horizontal
Glacial Striations (Maine)

16. M. Helper, Jackson School of Geosciences, UT Austin
Recording Trend and Plunge of a Line
Shorthand Notation:
“25o/150”
Reads:
“plunges 25
degrees toward a
bearing of 150o”
M. J. Cooke
Plunge = 25o
Horizontal
Trend = 150o