Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Law of included fragments
open-in-new
<p>The law of included fragments is a method of <a href="/facts/Relative_dating/PyvmNRU6">relative dating</a> in <a href="/facts/Geology/WGvVRIYF">geology</a>. Essentially, this law states that <a href="/facts/Clastic_rock/3y4SoUxl">clasts</a> in a rock are older than the rock itself. One example of this is a <a href="/facts/Xenolith/nP1MlHvG">xenolith</a>, which is a fragment of <a href="/facts/Country_rock_(geology)/e1kxFDsH">country rock</a> that fell into passing <a href="/facts/Magma/hRotHju9">magma</a> as a result of <a href="/facts/Stoping_(geology)/PtekRB2U">stoping</a>. Another example is a <a href="/facts/Derived_fossil/by7NzIA1">derived fossil</a>, which is a <a href="/facts/Fossil/by7NzIA1">fossil</a> that has been eroded from an older <a href="/facts/Bed_(geology)/vgEm2Y93">bed</a> and redeposited into a younger one. </p><p>This is a restatement of <a href="/facts/Charles_Lyell/6cAM8yRE">Charles Lyell</a>'s original principle of inclusions and components from his 1830 to 1833 multi-volume <i><a href="/facts/Principles_of_Geology/wA3UNkw2">Principles of Geology</a></i>, which states that, with <a href="/facts/Sedimentary_rock/HQDCjrco">sedimentary rocks</a>, if <a href="/facts/Inclusion_(mineral)/LtzBvP3p">inclusions</a> (or clasts) are found in a <a href="/facts/Formation_(stratigraphy)/mMhpw4G2">formation</a>, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for <a href="/facts/Gravel/IwHG9JfI">gravel</a> from an older formation to be ripped up and included in a newer layer. A similar situation with <a href="/facts/Igneous_rock/xeMJhUah">igneous rocks</a> occurs when xenoliths are found. These foreign bodies are picked up as <a href="/facts/Igneous_rock/xeMJhUah">magma</a> or <a href="/facts/Lava_flow/q2an5SVN">lava flows</a>, and are incorporated, later to cool in the <a href="/facts/Matrix_(geology)/dDgk5G1H">matrix</a>. As a result, xenoliths are older than the rock which contains them. </p>