Figure 12.18 A depiction of the strike and dip of some tilted sedimentary beds partially covered with water.В The notation for expressing strike and dip on a map is shown. Measurement of geological features is done with a special compass that has a built-in clinometer, which is a device for measuring vertical angles.В An example of how this is done is shown on Figure 12.19. if the strike is 0Лљ (i.e., north) and the dip is 30Лљ, it would be necessary to say вЂњto the westвЂќ or вЂњto the east.вЂќ Similarly if the strike is 45Лљ (i.e., northeast) and the dip is 60Лљ, it would be necessary to say вЂњto the northwestвЂќ or вЂњto the southeast.вЂќ It may help to imagine a vertical surface, such as a wall in your house.В The strike is the compass orientation of the wall and the dip is 90Лљ from horizontal.В If you could push the wall so itвЂ™s leaning over, but still attached to the floor, the strike direction would be the same, but the dip angle would be less than 90Лљ.В If you pushed the wall over completely so it was lying on the floor, it would no longer have a strike direction and its dip would be 0Лљ.В When describing the dip it is important to include the direction. Geologists take great pains to measure and record geological structures because they are critically important to understanding the geological history of a region.В One of the key features to measure is the orientation, or attitude, of bedding.В We know that sedimentary beds are deposited in horizontal layers, so if the layers are no longer horizontal, then we can infer that they have been affected by tectonic forces and have become either tilted, or folded.В We can express the orientation of a bed (or any other planar feature) with two values: first, the compass orientation of a horizontal line on the surface-the strike-and second, the angle at which the surface dips from the horizontal, (perpendicular to the strike)-the dip (Figure 12.18).

Geologic cross section example