Final answer:
Strike is a horizontal intersection direction of a rock layer, and dip is the layer's tilt angle. They are measured with a Brunton Compass and plotted on geologic maps using symbols.
Step-by-step explanation:
Strike and dip are geological terms used to describe the orientation of rock layers. A strike is the direction of the line formed by the intersection of a rock layer with the horizontal surface, while a dip is the angle at which the rock layer is tilted from the horizontal.
On a geologic map, strike and dip are plotted using symbols: a long line indicates the strike direction and a short line perpendicular to the strike line shows the dip direction, with the number representing the angle of dip.
Geologists use a Brunton Compass to measure these orientations accurately. When plotting these measurements, the strike is written first, followed by the dip angle and direction.
For example, 040/30 SE would indicate a strike of 40 degrees and a dip of 30 degrees to the southeast. The right-hand rule is commonly applied to ensure that the strike is perpendicular to the dip direction.
It is crucial for geologic maps to also include a scale and a north arrow. When creating a cross-section, aligning it perpendicular to the strike of the layers will display the true dip. If the cross-section isn't perpendicular, it will show an apparent dip, which is smaller than the true dip.