Most of those who live in or visit Northumberland will be very familiar with the two most prominent rock types. The rocks of the Whin Sill form many of the sea cliffs and provide a natural escarpment for Hadrian’s Wall; while sandstone outcrops are common around the uplands. But few will be aware that there are also substantial layers of the carboniferous era rock, The Great Limestone. This rarely outcrops on the surface but can be seen in several quarries around the Tyne Valley area. Of these Mootlaw Quarry is one of the largest. Now closed, it stretches nearly 1.5 miles between the villages of Ryal and Kirkheaton but it can be visited on a public bridleway which passes through the centre of the quarry.
The Carboniferous era (meaning coal-bearing), roughly 350 – 300 million years ago was the era, during different periods of which, there was both extensive sea-cover and huge marshy land masses. This led to the laying down of the materials both for limestone and coal, both of which were vital ingredients of the Industrial Revolution.
Within Great Britain the suite of rocks known traditionally as the Carboniferous Limestone Series was deposited as marine sediments.
The limestone visible at Mootlaw clearly shows several indications if its origin and its subsequent changes. The shales that overlie the Great Limestone are notable for a rich and varied fauna of brachiopods, molluscs, gastropods, crinoids and goniatites. The shales have also yielded an almost complete, fully articulated, crinoid: such fossils are almost invariably found in a fragmentary condition.
The limestone has been laid down in beds (layers) over long periods, which have different characteristics, with intervening beds of other materials . And there are many examples of folds ((Geological folds occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata are bent or curved as a result of permanent deformation).
To claim this cache you need to visit the quarry and answer a few questions which should NOT be included in your log but should be emailed to me. Logs may be deleted if an email has not been received. Photos are always welcome but not essential.
Parking is available at the road end (see additional waypoint) from where a short walk down the public bridleway will take you to the main coordinates. You do not need to cross the fence into the quarry as all the questions can be answered by viewing from the bridleway.
A rock face is visible immediately to your right and another one is visible further away and straight in front of you across the flooded area.
Look at the rock face on your right to answer the following
- How many limestone beds can you see?
- Estimate the height of the thickest one
- Describe any differences in the colour or appearance of the beds? Suggest some possible reasons for these differences
- What type of rock do you think makes up the thin dark bands between the limestone beds?
Now look at the rock face in the distance beyond the flooded area to answer the following
- The beds are not quite horizontal. What angle do you estimate the fall to be and in which direction does it run.
- What do you think may have caused the bed to slope?.