E&E 151 S Introductory Geology: Chapter 15.2 (Geologic Structures Pt. 2) Definitive Study

Geologic Structures

Structural features—such as folds, faults, and joints—within rock units that geologists map to locate ore deposits, evaluate seismic hazards, and guide engineering projects like dams and bridges.

Principle of Original Horizontality

The fundamental geologic principle stating that sedimentary layers, lava flows, and ashfalls are initially deposited as flat, horizontal beds. Any observed tilt occurred after the rocks were deposited and lithified.

Strike

The compass direction of the line created by the intersection of an inclined rock plane with an imaginary horizontal plane, customarily recorded in a northerly direction (e.g., N50°E).

Angle of Dip

The acute angle measured downward from a horizontal plane to the inclined bedding plane, measured inside a vertical plane perpendicular to both.

Direction of Dip

The compass direction in which a bed slopes downward (the direction a ball would roll down the surface), which is always at a 90° right angle (perpendicular) to the strike line.

Brunton Pocket Transit

A specialized geologic tool equipped with a compass, level, and inclination-measuring device to accurately record strike and dip measurements in the field.