Structures formed by waves

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Across
  1. 2. Section of a cliff left jutting out at the top
  2. 6. Measurement of large quantities of sand
  3. 7. A curved shape formed above an eroding hollow area
  4. 10. A hole formed by waves in the roof of a hollow
  5. 11. This long shape is left when the hollow collapses
  6. 13. Seawater draining back into the sea
  7. 15. pieces of a large rock
  8. 16. Synonym for the base of an eroding cliff
  9. 17. Hot humid area near the Equator
Down
  1. 1. Parts of a fish that wear away to make sand
  2. 3. Hard substance from skeletons of tiny sea animals
  3. 4. Gentle sloping areas of sand near the ocean
  4. 5. A tiny piece of sand
  5. 8. materials that make a beach
  6. 9. Most sand is made from this material
  7. 12. Hollow area found inside a cliff
  8. 14. Beach formed from wind blowing debris
  9. 15. Sections of a cliff base made of soft rock