Question

The diagram above shows several rock layers and other geologic features. Each feature is labeled with a unique letter. The order of the letters do not necessarily reflect the order in which the features formed. Examine the diagram, and answer the question that follows. Using the principles of original horizontality, superposition, and cross-cutting relationships, determine which of the following features is the youngest.

(1 point)
Responses

N
N

G
G

R
R

H

Answer 1

I can’t tell which letter is youngest without seeing the diagram. Please upload the image (or describe which features cut which layers, which lie on top, and any intrusions/unconformities), and I’ll pick the youngest.

Meanwhile, here’s how to determine it yourself:

1. Superposition: in an undisturbed sequence, the topmost sedimentary layer is youngest.
2. Original horizontality: layers were deposited horizontal; tilting/folding happened after deposition.
3. Cross‑cutting relationships: any fault, dike, or other feature that cuts across rocks is younger than the rocks it cuts.
4. Inclusions: rock fragments inside a rock are older than the host rock.
5. Baked/contact metamorphism: the rock that is baked by an intrusion is older than the intrusion.

So find the feature that either (a) sits on top of all others, or (b) cuts across all the other units — that feature is the youngest. If you upload the diagram I’ll apply these rules and give the correct letter.