Laboratory Manual for Introductory Geology 4e

FIGURE 10.2 Geology of Sheep Mountain in Wyoming.
Hard sandstone
Soft
shale
(b) Block diagram.
(a) Oblique aerial photo.
(c) Cross section.
N
Youngest
Oldest
0
1 mi
0
1 km
(d) Geologic map. The color bands represent rock units. The map corresponds to the photo in part (a)—
though it is rotated approximately 43° clockwise.
formation (a sequence of sedimentary and/or volcanic layers that has a definable
age and can be identified over a broad region), an igneous intrusion, or an interval
of a specified type of metamorphic rock. Geologists recognize several types of contacts:
(1) an intrusive contact is the boundary surface of an intrusive igneous body;
(2) a conformable contact is the boundary between successive beds, sedimentary
formations, or volcanic extrusions in a continuous stratigraphic sequence; (3) an
unconformable contact (or unconformity) occurs where a period of erosion and/
or nondeposition has interrupted deposition; and (4) a fault contact is where two
units are juxtaposed across a fault. Throughout this chapter, you’ll gain experience
interpreting contacts, but to be sure you understand these definitions from the
start, complete Exercise 10.2.
242 CHAPTER 10 INTERPRETING GEOLOGIC STRUCTURES