Does the law of inclusion and the law of crosscutting indicate that bottom layers are older, or do they indicate that intruding objects are younger?
The principles you are referring to are called the Law of Inclusion and the Law of Crosscutting Relationships, which are important principles in relative dating used by geologists and archaeologists to determine the order of rock layers or the sequence of events.
1. Law of Inclusion: This principle states that in a sequence of sedimentary rock layers, any rock fragments (inclusions) contained within a rock layer must be older than the rock itself. This is because the inclusions are derived from pre-existing rocks that were weathered or eroded before being deposited and buried within the new rock layer. Therefore, the law of inclusion suggests that the bottom layers are generally older than the layers above them.
2. Law of Crosscutting Relationships: This principle states that any geological feature or rock formation that cuts across another rock unit is younger in comparison. This can apply to igneous intrusions (e.g., veins or dikes) cutting through existing rock layers, faults that offset rock layers, or erosional features like canyons or valleys that have been carved into existing rock formations. The principle suggests that the intruding objects or geological features are younger than the rocks they cut across.
So, to answer your question, the Law of Inclusion indicates that the bottom layers are generally older, while the Law of Crosscutting Relationships suggests that the intruding objects or geological features are younger. These principles help geologists create relative chronological sequences of events, but they do not provide precise ages. For absolute dating, other methods such as radiometric dating are used.