Geologic Time: Concepts and Principles - The Changing Earth: Exploring Geology and Evolution - page 441

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Figure 17.5 The Principle of Inclusions

a The sandstone is older than the
granite batholith because there are
inclusions of sandstone inside the
granite. The sandstone also shows
evidence of having been baked along its
contact with the granite batholith when
the granitic magma intruded the overlying
sedimentary beds.

1 2

Sandstone
bed

Baked zone

Sandstone
bed

Sandstone
inclusions

Granitic
magma

Granite
batholith

The sandstone is younger than the
granite batholith because it contains
pieces (clasts) of granite. The granite is
also weathered along the contact with
the sandstone, indicating that it was the
source of the granite clasts, and must
therefore be older than the sandstone.

b

1 2

Granite clasts

Sandstone
deposition

Sandstone
bed

Sandstone
bed

Weathering
zone

Granite
batholith

Granite
batholith

Outcrop in northern Wisconsin showing basalt
inclusions (dark gray) in granite (white). Accordingly, the
basalt inclusions are older than the granite.

c

Granite

Basalt
inclusion