Cross Hill Quarry EarthCache

Once quarrying at Cross Hill ceased, the thin soils and exposed rock became re-vegetated through stages of succession from flower-rich grasslands, to hawthorn scrub and finally woodland. Examples of each stage can still be seen. If you visit in June you will see the fine display of wildflowers in the main quarry.

The quarry floor is made up of mounds of spoil and is rich in lime. This provides perfect growing conditions for many limestone grassland flowers. Fairy Flax, the lemon flowered Mouse-ear Hawkweed and Lady's Bedstraw can be found along with fragrant herbs such as Wild Thyme and Marjoram. 

In the eastern end of the reserve, another quarry was in filled in the 1970's and heavy clay used as a capping. Here you will find Hard Rush, Soft Rush, Reed Canary-grass and Willows flourishing. However, this area has also developed a healthy population of Common Spotted and Northern Marsh Orchids. In the dense shade under the scrub, ivy forms thick carpets covering the hollows and mounds.  

Most woodland flowers need more light and Cuckoo-pint (Lords-and-ladies), Dog's Mercury, Lesser Celandine, Hedge Woundwort and Wild Rose are found closer to the paths. Bluebells, Wood Anemone, Woodruff and Wood Sanicle can be found in the more open, undisturbed western woods towards Brungerley Park, which were never quarried. 

The given co-ordinates bring you to the main quarry face, showing the exposed limestone laid down in bedding planes, which have been tilted over the period since they were first laid down millions of years ago. The quarry itself produced Chatburn Limestone and you can see here about 40m depth on the exposed cliff face. However, the limestone here is actually approximately 840m deep.

To give a brief history of the rocks that you are seeing here, these rocks are limestone and they were created millions of years ago in warm seas near the Equator. Sometimes rivers carried mud and silt into sea where it was laid down as thin beds and the sea was a living environment vibrant with life. Over a great length of time, these layers became rock and then at some point they were pushed by a great force from the south-east which tipped them up. Very slowly, the rocks were moved from the tropics where they formed nearly 5000 kilometres to Clitheroe. At some time the rocks emerged from the sea and were worn down by rivers and glaciers to their present level. This entire process happened very slowly - over 300 million years.

As you look at the quarry face you will see many grey rocks. These usually contain lots of calcium – this is the chemical element that sea shells, teeth and bones are made from. The thin brown bands are deposits of silt and mud, which must have been carried by rivers into the sea from a nearby land mass.

These rocks were folded at the end of the Carboniferous period by a plate moving from the SE. This created the Ribblesdale Fold Belt which was later eroded down to the level of the quarry. This now provides a window into one side of one of the folds – the Horrocksford Anticline or upfold.

Geologists approach the age of rocks in two different ways. One is to arrange the layers in order of their age - older ones at the bottom and younger ones at the top. This is a relative age scale. They use fossils which are widespread and have evolved rapidly to determine the relative age of rocks.

The best fossils for this identification in the Chatburn Limestone found here at Cross Cliff Quarry are corals and brachiopods. When the fossils found in rock beds many miles apart are identical, geologists can infer that both beds of rocks are the same age. The other way to date rocks is to use radiometric methods, like Carbon14 dating, to fix the absolute age. The Chatburn Limestone rocks at Cross Hill are among the earliest rocks of Carboniferous age in Britain and are 340 to 350M years old.

You may be wondering why there are so few fossils to see here at Cross Hill Quarry. Anywhere on Earth, the number of organisms that can survive depends on how much food there is to eat. It was probably quite scarce in the sea where these rocks were made. Also, there was a food chain so many organisms were eaten by other animals which in turn were eaten by others leaving little to see.

The flower-rich grasslands of the main quarry attract a number of butterflies. The Small Skipper, with its moth like appearance, the Orange Tip, in which only the male has orange wing-tips, and Meadow Browns are frequent residents on this site. 

Bird activity can be observed all year round at Cross Hill. In spring the Blackcap, Willow Warbler and Chiffchaff all return from warmer climates with Grey Wagtails and Sand Martins very evident from April onwards on the adjacent River Ribble. The river also provides feeding ground for birds such as Herons, which are often seen along the river, and Kingfishers throughout the year. 

The reserve is a good site for bats with plenty of woodland edge and open areas for hunting Pipistrelles. Noctules are also present whilst Daubenton’s can be seen skimming over the surface of the river. 

The site is in the care of the Wildlife Trust, who have kindly granted permission for this earthcache to be published. Please respect the nature reserve by keeping to the paths and avoiding interfering with the plants. No climbing on this cliff face is permitted without first obtaining permission from the Wildlife Trust, to avoid interference with the wildlife. Many thanks also to the Wildlife Trust for providing much of the information in this listing.

Please send the answers to the below questions using the 'email' facility in my profile. Do not post the answers in your log or it would unfortunately have to be deleted. Please make your best effort to answer the questions correctly, I will contact you if there are any problems with your answers. Please try and send your answers at the same time as submitting your log or very soon afterwards.

1. Please observe the rock face and tell me whether the rock here is igneous, sedimentary, or metamorphic? Why?
2. Have a look at the rock layers and estimate the width of the thinnest and the thickest layers you can see. Where are they located – to the top or bottom of the quarry face and do you believe there is any particular reason for this position?
3. Measure the ‘Angle of Dip’ of the rock layers. You can download a free app on any smartphone to do this task, or look up how to make a ‘Clinometer’ for yourself on the web.  
4. Each metre of rock that you can see here took (very roughly) ten thousand years to accumulate, please tell me how many years approximately it would have taken for the exposed quarry face you can see here to have formed.
5. As explained above, in the eastern area of the reserve you find species such as rushes, reed grass and marsh orchids. How has the clay cap affected the soil to encourage these species?
6. A photo or you or your GPSr with the cliff face or anywhere in the reserve would be good further proof of your visit - this is an optional task.

Igneous
Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.

Sedimentary
Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils.

Metamorphic
Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface.