2.3 Geological principles

Question 1

What are the key principles?

Answer 1

1. Uniformitarianism
2. Principle of original horizontality (POOH)
3. Lateral continuity
4. Law of superposition
5. Law of included fragments
6. Law of cross cutting relationships

Question 2

What is uniformitarianism?

Answer 2

The present is the key to the past
Today’s rock forming processes must have been same as processes in the past
Eg if coral was found in a rock it must have formed in a shallow tropical seas
Eg if large a scale cross bed is found in a rock it must have been formed in a windy desert

Question 3

What is original horizontality?

Answer 3

We assume all sedimentary rocks are deposited horizontally

Dipping rocks are laid at an angle and assumed to be older than horizontal rocks

Question 4

What is lateral continuity?

Answer 4

All rocks are continuous sideways unless cut by another structure such as a fault or unconformity

Question 5

What is the law of superposition?

Answer 5

Oldest rocks are always at the bottom (deeper) unless the rocks have been overturned
Sedimentary structures of rocks help indicate if a sequence of rocks have been overturned, way up criteria
Eg flute casts, flame and load, desiccation cracks, cross beds

Question 6

What is the law of included fragments?

Answer 6

If a rock contains fragments of another rock then the fragments must be older than the rock they are found in

Question 7

What is the law of cross cutting relationships?

Answer 7

If a rock or structure cuts across another rock or structure, the rock which cuts across must be younger

THE ROCK THAT CUTS ACROSS MUST BE YOUNGER