Geologists conclude that the clasts in layer a are older than the layer itself. which geologic principle do the geologists use to draw this conclusion?

C. Principle of inclusion

Explanation:

One of the principles used to date a rock relatively is using "principle of inclusion".

The principle of inclusion states that " the fragments included in the host rock are older than the rock itself".

The fragment of rocks in the sedimentary layer A are older than the rock layers itself. If we encounter the main rock where the fragment is derieved is older than layer A itself.

The principle asserts that for us to have those fragments of rocks in the layer A, the fragments must have been derieved from rocks that have already formed. Therefore, that rock is older than the sedimentary layer.

Principle of original horizontality states that "beds of sedimentary rocks formed as horizontal or horizontal layers".

Principle of superposition states that "in an undeformed or undisturbed sedimentary sequence, the older rock is at the bottom of the sequence".

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

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