In the context of geology, what does the term 'inclusion' refer to?

The term 'inclusion' in geology specifically refers to fragments of one rock type that are found within another rock type. This concept is vital for understanding the relationships between different rock types and their formation processes. When a rock with inclusions forms, it incorporates pieces of older rocks, suggesting that the rock host is younger than the included material. This principle is used in interpreting geologic history and helps geologists to establish the relative ages of rocks, making it a fundamental aspect of stratigraphy and geological time.

In contrast, other choices pertain to different geological principles. The mention of sequences of geological features refers to stratigraphic layering rather than the specific notion of inclusions. Layers of sediment deposited horizontally describe sedimentary processes but do not directly relate to the concept of inclusions. Lastly, types of minerals involved in rock formation relate to mineralogy and the composition of rocks rather than the interaction between different rock types that inclusions highlight. Hence, the correct understanding of 'inclusion' focuses on the presence of fragments within a host rock, marking the relationships between different geological materials.