The great expanses of purple heather that swathe the upper moorland of the North York Moors are one of the most famous scenes in the National Park. Yet underlying the peat is a story just as fascinating.
The rocks here are around 170 million years old, from the Middle Jurassic period. They were deposited by great rivers flowing from the north, and these sand banks and swamps were home to a rich plant life including giant horsetails, cycads and monkey puzzle trees (the latter the source of Whitby jet). The plant life, in turn, supported a whole community of animals dominated by the dinosaurs. Although dinosaur bones are rare here, dinosaur footprints are relatively common and are among the most important fossils found in the area.
The underlying sandstone provides the building stone that characterises the villages, and is also responsible for the poor quality of the soil on the moors. The bottom of the dales are often more fertile due to the presence of lower Jurassic shales.
Dales and gorges
For the last 65 million years the whole of the North York Moors has been rising up to form the uplands we see today. These uplands are cut through by numerous dales, which often contain a small beck or river in the bottom that looks far too small to have carved such a large valley. In many cases the dales were carved by torrents of meltwater from overflowing glacial lakes that only flowed for a few hundred years – the present river is simply following the old watercourse.
Newtondale starts in the centre of the North York Moors and is one of the finest examples of a meltwater channel in the country. Many other dales, including Bilsdale and Farndale, were also cut by glacial meltwater overflowing from the north.
The Cleveland Dyke
The Cleveland Dyke is a remarkable feature of the central moorland. This line of hard igneous rock was injected into the area 58 million years ago as huge volcanoes erupted on the Isle of Mull in Scotland. Today much of this feature is a great trough as the hard rock has been quarried for road stone.
The stone of the central moorlands has been used for many purposes. The sandstones not only make good building material but were also once used for millstones to grind corn. The thin coals formed by the rich plant life were exploited by successive generations and the waste tips can be seen in various locations.
One of the most imposing sites in the National Park is Rosedale with its derelict ironstone workings. These were mined for Jurassic ironstones that were first deposited over 150 million years ago.