This is one of a series of EarthCaches placed at sites within the Westmorland Dales area which the Cumbria GeoConservation group considers as being good examples of various aspects of the local geology. Our geological research has been made possible by the Westmorland Dales Landscape Partnership Scheme, jointly led by the Friends of the Lake District and the Yorkshire Dales National Park Authority and has been grant funded by the National Lottery Heritage Fund.
In contrast to the limestones typically seen In the Westmorland Dales, here we have a thick layer of sandstone, the Ashfell Sandstone. At the time when these rocks were deposited, in the early Carboniferous Period about 350 million years ago, the land that is now Britain was situated just north of the Equator. Most of the time, the area was flooded by a shallow sea, teeming with life and with lime particles accumulating at the bottom, which later became limestone. To the north of the sea was a large continent with mountains, and with rivers running from them down to the sea. These rivers carried a lot of sand eroded from the mountains and when they entered the sea, they formed huge deltas. In these deltas, the river would break up into many small channels running across the delta top. The sandstone that we see here is a record of the sand deposited in these channels on a delta that spread into the sea over the limestone. As the sand grains were pushed along by the water current, they formed sloping layers called cross-beds, as shown in this diagram.
© E Pickett
Over time, the sand grains have been cemented together, making a very hard rock which can be used as a strong building stone. At this outcrop, you will see that the sandstone has been weathered into rounded shapes. Look over the wall to see some in the nearby fields.
Questions:
To claim this EarthCache, please send your answers in a message, either by e-mail or through the Message Centre. Do not put them in your log. You do not have to wait for a reply before logging; if there is a problem with your answers we will let you know. Pictures of your visit are very welcome in your log, but please avoid giving away any of the answers.
1. Roughly what thickness of sandstone overall is exposed in this small quarry? Is this the full thickness of the sand deposited at this position in the delta?
2. Look at the cross bedded layers in the sandstone, similar to those shown in the diagram above. How thick are the cross-bedded layers in the rock? Was the water current always flowing in the same direction?
3. The rusty red colour of the rock is due to iron oxide. Are the grains red or does the red colour appear to be in the cement that holds the grains together or are both the grains and the cement red? Are there any pebbles in amongst the sand?
4. When this rock was being quarried, will it have broken easily into blocks to use for building stone? Explain your answer.