Rock Layers Vocabulary

Unconformity

Contact between rocks that are sedimentary that are significantly different in age, or between sedimentary rocks and older , eroded igneous rocks or even metamorphic rocks.They represent gaps in the geological record. Looking at this image you can most likely pick out the ages of rock and what types of rock they could be.

Crosscutting Relationships

Crosscutting relationships is a principle that states that an igneous intrusion is always younger that the piece of rock that it cuts across. A fault where the Ayes move is also younger than the layers that are already there. The image shows how there is two young ones and one old one. The old one on the bottom and the young on the top and the cut between them young also.

Principle of Original Horizontality

States that all the layers of sediment were originally deposited horizontally because of gravity. The photo shows how they were once horizontal, and now aren't so much.

Principle of Inclusions

States that if inclusions or clasts are found in the formation of sedimentary rock than the inclusions must be older than the actual formation that contains them. The image shows a sill and flow inclusion.

Principle of Superposition

The concept that states that the oldest rock layers are towards the bottom of the sequence and the the younger rock layers are deposited on top of them. This however, can be considered as a rule that applies in all situations, only except where the rocks are to an extreme deformed, different shaped, etc. The image shows a quick fact about the Principle of Superposition, since it means the older the layer the farther down it will be, it's saying the deeper you did, the older the fossil.

Relative Age

The geologic age of anything from an organism to a rock or even a geologic feature that is relative to others.Determining the realative order or past events. Approximate age (not exact). The picture shows the different layers and how old they were. Also, if they were younger or older.

Index Fossil

The remains of an organism that once was living in a geologic age which is used to identify and date (find out how old it was made or is) the rock or rock layer that it was found in. The photo shows that different types of shells were found in different layers. This gave geologists clues on about how old they were if they matched up.