Geological history
The oldest rocks within the National Park are Lower Jurassic, 200 million years old. These are the dark coloured shales and limestones that can be seen along the coastline at places like Robin Hood's Bay in the cliffs and from Whitby north to Saltburn. They were deposited in a great ocean that covered much of Europe at the time. This sea was home to a huge variety of life, the famous ammonites were among the most common animal and they provided food for great marine reptiles, cousins of the land based dinosaurs. Long necked plesiosaurs would have patrolled the depths along with marine crocodiles and ichthyosaurs.
By around 170 million years ago, in the Middle Jurassic period, the sea level had fallen and the area was covered in great river channels and swamps. These conditions formed the thick sandstones that outcrop along the coast above the Lower Jurassic shales and form the bedrock of the central moorland. The deltas were rich in plant life, including giant horsetails, ginkos, and monkey puzzle trees, the latter being the source of Whitby jet. This plant life provided food for herbivorous dinosaurs that in turn provided food for carnivorous theropod dinosaurs. These dinosaurs have left behind hundreds of footprints that have led to the coastline being called the Dinosaur Coast.
The Upper Jurassic, around 150 million years ago, saw the return of the ocean to the area as sea levels rose. These waters deposited the limestone that forms the Tabular Hills. The shallow seas were full of ammonites, fish and reptiles while the sea beds were home to great coral reefs.
Great changes to the landscape of the North York Moors occurred during the Ice Ages. During the last ice age which peaked around 20,000 years ago, the area was bordered to the North, East and West by ice sheets often hundreds of metres thick. The area still bears hallmarks of this time, the most dramatic of these being the great overflow channels where glacial lakes and meltwater broke through low points in the landscape to carve deep and steep sided valleys such as Newton Dale and Forge Valley.
