Geologic Time: Concepts and Principles - The Changing Earth: Exploring Geology and Evolution - page 438

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Figure 17.2 The Principles of Original Horizontality,
Superposition, and Lateral Continuity

Figure 17.3 The Principle of Cross-Cutting Relationships

The sedimentary rocks of Bryce Canyon National Park, Utah,
were originally deposited horizontally in a variety of continental
environments (principle of original horizontality). The oldest
rocks are at the bottom of this highly dissected landscape, and
the youngest rocks are at the top, forming the rims (principle of
superposition). The exposed rock layers extend laterally in all
directions for some distance (principle of lateral continuity).

a

A dark gabbro dike cuts across granite in Acadia National Park,
Maine. The dike is younger than the granite that it intrudes.

a

These shales and limestones of the Postolonnec Formation,
at Postolonnec Beach, Crozon Peninsula, France, were originally
deposited horizontally, but have been signifi cantly tilted since their
formation.

A small fault (arrows show direction of movement) cuts across,
and thus displaces, tilted sedimentary beds along the Templin
Highway in Castaic, California. The fault is therefore younger than
the youngest beds that are displaced.

b

b