The Country Park lies on a sandstone ridge comprising red sandstone and conglomerate pebble beds laid down in the Lower Triassic period (some 215 to 250 million years ago) when Britain lay just north of the equator. The environment at the time was that of a hot arid desert and the sandstone and pebble beds were deposited on the ancient landscape by flash floods and intermittent rivers. It is possible that each bed of pebbles was laid down in one event over a short period of days or weeks rather than years.
The pebbles seen here are quartzite (a hardish reddish/grey rock), quartz (a hard grey/white mineral) as well as granite (with interlocking crystals of feldspar, quartz and mica), and porphyry (a pinkish rock with scattered crystals of feldspar and quartz). All the pebbles are well rounded showing they have been transported long distances by water; and the granite and porphyry pebbles originated in what is now the South West of England and North West of France.
As the flash floods subsided, very thick layers of sands and gravels were deposited as horizontal bars on the beds of wide river channels, with finer materials settling out in quieter waters. Evidence of these beds can be seen in the quarry faces. At the edge of sand or gravel bars the moving sediments avalanche down the slopes and can now be seen as diagonal lines in the rock termed cross-bedding.
Over millions of years of later earth movements, the rocks have been uplifted, tilted, faulted and eroded, long before quarrying began here less than 100 years ago. Now these excellent exposures of river-born deposits, exposed by quarrying, offer a unique opportunity to view the sequence of sandstone and pebble beds and in 2002 the old quarries were designated a Site of Special Scientific Interest (SSSI) and a National Nature Reserve (NNR) – one of the very few NNRs designated for their geology.
Please do not damage the rock faces, there are plenty of loose pebbles at the foot of the cliffs.
Park at the Visitor Centre Car Park (N53° 0.015' W2° 6.351') – accessed via Hulme Road. Then walk to N53° 0.005' W2° 06.260' to get an overall view of the quarry sides.
Now walk along the path to N53° 0.045' W2° 6.202'. Look at the rock face here to see the different beds of sandstone and pebble stone.
Q1: How many layers are there?
Q2: Estimate the total height of the rock face.
Now walk along the rock face to N53° 0.087' W2° 6.223'. If you look at the rock face here you can see diagonal lines in the sandstone. This is called cross-bedding and indicates the direction that the river was flowing as the higher side will be upstream.
Q3: Which direction was the river flowing?
Walk to N53° 0.122' W2° 6.259' and let your eye follow the layers of rock along the rock face. Suddenly, you find that there is a discontinuity. This is caused by an ancient fault, where the beds to the west have dropped down by several metres.
Q4: What is the angle of the fault line to the vertical?
(The fault is what made further quarrying uneconomic as the pebble beds on the east face could not be removed unless the layers of sandstone above them were also removed.)
Please click on my name at the top of this page to email the answers to the above questions when you log your visit. Any logs which are not accompanied by an email may be deleted without further warning.
Congratulations to Ivan for logging this cache first!!!