Thinking Skills
Four rock layers — Clay, Granite, Limestone, and Sandstone — form a cliff face, stacked from layer 1 (bottom)…
Question 1 · Multiple choice
Question
Four rock layers — Clay, Granite, Limestone, and Sandstone — form a cliff face, stacked from layer 1 (bottom) to layer 4 (top). Each layer occupies exactly one position.
- Clay is placed directly below Granite (no other layer is between them).
- Sandstone is placed somewhere above Granite.
- Limestone is not the bottom layer or the top layer.
Which of the following shows a valid order from bottom (layer 1) to top (layer 4)?
Options
- A.Clay, Limestone, Granite, Sandstone
- B.Sandstone, Granite, Clay, Limestone
- C.Clay, Granite, Limestone, Sandstone
- D.Granite, Clay, Limestone, Sandstone
Correct answer
Explanation
Step 1: Understand the setup
We have 4 rock layers stacked in a cliff face. Layer 1 is at the BOTTOM and layer 4 is at the TOP.
Layer 4 ←── TOP (highest)
Layer 3
Layer 2
Layer 1 ←── BOTTOM (lowest)
Each layer holds exactly one type of rock. We need to find which of the four arrangements obeys ALL of the clues.
Step 2: Write out the clues carefully
-
Clue 1: Clay is DIRECTLY BELOW Granite. This means Clay and Granite must be NEXT TO each other, with Clay one step below. For example: Clay at layer 2, Granite at layer 3. ✓ NOT okay: Clay at layer 1, Granite at layer 3 — that has a gap between them. ✗
-
Clue 2: Sandstone is somewhere ABOVE Granite. Sandstone's layer number must be greater than Granite's — but they do NOT need to be next to each other.
-
Clue 3: Limestone is NOT the bottom layer (layer 1) or the top layer (layer 4). Limestone must be in layer 2 or layer 3.
Step 3: The checking method
For each arrangement, we will test ALL THREE clues in order. If even one clue fails, that arrangement is wrong. We move on to the next.
Step 4: Check Option A — Clay, Limestone, Granite, Sandstone
Layer 4: Sandstone
Layer 3: Granite
Layer 2: Limestone
Layer 1: Clay
Check Clue 1 — Is Clay directly below Granite (no gap)? Clay is at layer 1. Granite is at layer 3. The gap between them: layer 2 (Limestone) is in between. NOT directly below. ✗
Option A fails on Clue 1. Move on.
Step 5: Check Option B — Sandstone, Granite, Clay, Limestone
Layer 4: Limestone
Layer 3: Clay
Layer 2: Granite
Layer 1: Sandstone
Check Clue 1 — Is Clay directly below Granite? Clay is at layer 3. Granite is at layer 2. Clay is ABOVE Granite, not below. ✗
Option B fails on Clue 1 (and also breaks Clues 2 and 3, but one failure is enough). Move on.
Step 6: Check Option C — Clay, Granite, Limestone, Sandstone
Layer 4: Sandstone
Layer 3: Limestone
Layer 2: Granite
Layer 1: Clay
Check Clue 1 — Is Clay directly below Granite (no gap)? Clay is at layer 1. Granite is at layer 2. They are next to each other, and Clay is one step below. ✓
Check Clue 2 — Is Sandstone above Granite? Sandstone is at layer 4. Granite is at layer 2. 4 > 2, so Sandstone is above. ✓
Check Clue 3 — Is Limestone NOT at the bottom or top? Limestone is at layer 3. Not layer 1, not layer 4. ✓
All three clues pass! Option C is valid. ✓
Step 7: Check Option D — Granite, Clay, Limestone, Sandstone
(We check this anyway to be thorough.)
Layer 4: Sandstone
Layer 3: Limestone
Layer 2: Clay
Layer 1: Granite
Check Clue 1 — Is Clay directly below Granite? Clay is at layer 2. Granite is at layer 1. Clay is ABOVE Granite — but the clue says Clay must be BELOW Granite. ✗
Option D fails on Clue 1.
Step 8: Summary of all checks
Option | Layout (bottom → top) | Clue 1 | Clue 2 | Clue 3 | Result
───────┼─────────────────────────────────────┼────────┼────────┼────────┼───────
A | Clay, Limestone, Granite, Sandstone | ✗ | — | — | FAIL
B | Sandstone, Granite, Clay, Limestone | ✗ | — | — | FAIL
C | Clay, Granite, Limestone, Sandstone | ✓ | ✓ | ✓ | PASS ✓
D | Granite, Clay, Limestone, Sandstone | ✗ | — | — | FAIL
Key lesson — "directly below" vs "somewhere above"
"Directly below" = must be NEXT DOOR with no gap
Layer 3: Granite
Layer 2: Clay ←── directly below Granite ✓
Layer 3: Granite
Layer 2: (something else)
Layer 1: Clay ←── NOT directly below (gap in between) ✗
"Somewhere above" = just needs to be higher, gap is fine
Layer 4: Sandstone ←── somewhere above Granite ✓
Layer 3: Limestone
Layer 2: Granite
The answer is Option C: Clay, Granite, Limestone, Sandstone.