Foundation Geology

After completing this 10-part series, you have transitioned from a beginner to someone with a basic understanding of how hundreds of millions of years of history created the modern Sidmouth landscape.

Here are the ten key facts you have learned:

1. Sidmouth is an "Ancient Desert": The iconic red colour of the cliffs comes from iron oxide (rust), proving that 240 million years ago, Sidmouth was located near the equator in a scorching, arid desert.

2. The "Layer Cake" of Rocks: The local landscape is built of three primary layers: the Otter Sandstone (bottom), the Sidmouth Mudstone (middle), and the Upper Greensand (top).

3. A 140-Million-Year Gap: You learned about the "Great Unconformity," a geological mystery where the rock record jumps directly from the Triassic (240 Ma) to the Cretaceous (100 Ma), with the entire Jurassic period missing due to erosion.

4. The Cause of Landslides: You now understand that landslides happen because the porous Greensand on top acts like a sponge, trapping water against the waterproof Mudstone below, creating a slippery "slip plane."

5. Life Before Dinosaurs: The Otter Sandstone is a world-class site for fossils of Triassic reptiles like Rhynchosaurs and giant amphibians that lived long before the famous dinosaurs of the Jurassic.

6. The "Great Dying": You learned that the Permian period ended with the most catastrophic extinction in Earth's history, wiping out 96% of marine life and paving the way for the "Age of Reptiles."

7. Pangea’s Breakup: You discovered how the supercontinent Pangea split apart, shifting the climate from desert to the shallow tropical seas that deposited the Mercia Mudstone.

8. Industrial History: You learned that our local rocks aren't just for looking at—they built the great West Country cathedrals (Exeter and Salisbury) and were used for brickmaking and salt mining.

9. The "Green" in the Sand: You know that the green hue in the top layers of the hills comes from a mineral called Glauconite, which only forms in specific marine environments.

10. Natural Defenses: Finally, you learned that the shingle (pebbles) on the beach acts as a natural "shock absorber," protecting the town and the fragile cliffs from the raw power of the English Channel.

By understanding these ten facts, you can now "read" the cliffs of Sidmouth like the pages of a history book!