| Clue | Source | Date |
|---|---|---|
| Type of porous rock (obs) (4) | ||
| Soft porous rock consisting of calcium carbonate deposited from springs rich in lime | Mirror Quiz | 09 Feb 2025 |
| Porous limestone | The Telegraph Cross Atlantic | 20 Nov 2024 |
| Soft porous rock consisting of calcium carbonate deposited from springs rich in lime | Mirror Quiz | 12 Nov 2024 |
| Porous limestone created by precipitation (4) | The Guardian Quick | 25 Jul 2024 |
| Porous rock (A, not F) | The Times Concise | 13 Jan 2015 |
| Soft, porous rock | ||
| Lime spring deposit | ||
| Porous limestone | ||
| Limestone deposite | ||
| Porous rock | ||
| Porous rock | ||
| Geyseral deposit | ||
| Porous rock. | ||
| Volcanic rock. | ||
| Soft, porous rock. | ||
| Porous limestone. | ||
| Volcano rock. |