When you next take a stroll along the Pier at Whitby, stop at the light house, and look back towards the town. You will notice that the cliffs on either side of the pier look very different to each other. Why?
THE EAST CLIFFS
The East Cliffs have lots of horizontal layers of dark and light rock—shales and sandstones.
The grey Alum Shales (in the bottom half of the cliffs) are the source of the famous fossils of Whitby. They are rich in the fossilized remains of creatures which lived in the warm shallow seas of Yorkshire during the early Jurassic period (around 206 million years ago). Ammonites, belemnites and a variety of sea shells are commonly found washed up on the beach.
Fossilised reptiles (evidence of deeper seas above Yorkshire 190 million years ago!), such as plesiosaurs and ichthyosaurs, have also been found.
Above the shales, there is a layer of Jet (used locally for jewellery), which is fossilised wood from trees and branches preserved in swaps. Other plant and tree fossils in the upper cliffs show that Whitby was on dry land again by the mid-late Jurassic.
THE WEST CLIFFS
The West Cliffs are very “messy-looking” compared to the “tidy” layers in the East Cliffs.
The rock is all the same pale yellowy-red colour, and if you have a closer look at it, it consists almost entirely of sand stone.
There are broken pieces of fossilised plants and wood in the cliffs, some no bigger than little black specks in the sand.
All of these things are very important, as they are indications that the sand was transported and laid down by fast-flowing rivers and deltas across land—just like we see them today!
WHITBY: Both on land AND under the sea?!
So far, we have evidence of Jurassic sea life on one side and land vegetation on the other — but Whitby cannot possibly have been under the sea and above it at the same time!
The answer lies below the river Esk: there is a fault running between the East and West Cliffs: Whilst the sand was being deposited in horizontal layers on the East Cliff, the West Cliff was being forced down by the fault.
The more it descended, the more water was drawn towards it in rivers. The rivers carried the sand and plant fragments, and these were dumped at the bottom of the river beds on the way to the sea.