Lickey Quartzite quarry
This quarry is not open to the public, but it is cut into the side of the Lickey Ridge and allows us to see the rock that the hill is made from. It is a very hard rock called Lickey Quartzite. It is likely that stone chippings on the path here of Lickey Quartzite, so you could pick a bit up to look at it closely. The rock is composed of sand-sized grains of the mineral quartz, one of the hardest minerals. Lickey Quartzite is such a hard rock that it was quarried in the 19th and 20th centuries for use in building roads and for the construction of the Frankley Reservoir, which receives water from Wales via the Elan aqueduct.
The Frankley Reservoir, built in 1904, holds 900,000 cubic metres of drinking water for Birmingham. It did leak 540 litres per second until the fault was detected and put right in 1987.
It is thought that the Lickey Quartzite started out as sand on the shore of a shallow sea some 480 million years ago. Layer upon layer of it built up over millions of years. Later it was buried by more sediments and liquids passing through the beds of sand deposited more quartz to act as a ‘glue’ or cement between the grains. Later, buried deep in the earth, the rock was subject to heat and pressure, which recrystallized the quartz grains and cement, binding the rock even more solidly together.
The photo below is a close-up of the Lickey Quartzite in the quarry. Note how the beds of rock are now dipping at a steep angle as a result of massive tectonic forces they have been subjected to.
One of the rock beds in the quarry has an undulating surface. The inset picture shows this same feature from another location where it is a bit easier to spot. These are actual ripples that formed on the sand of the sea shore, 480 million years ago in the Ordovician period of geological time. The following fro the app user > Touch ‘then’ to see what this place was like in Ordovician times. Touching the globe icon will show you where on the planet we were. The ‘i’ tab will give you environmental information and the ‘life’ icon will show you what creatures you may have encountered! Touch the North arrow to return to the image of the Ordovician sea shore.
The inset picture of ripples on a rock bed is from near the Wrekin in Shropshire, and features a beach, or shallow sea water environment, from around 544 million years ago at the start of the Cambrian Period.
In some parts of the Lickey Hills there are thin, purple-grey clay layers between the beds of quartzite. It is thought (although not confirmed) that the clay may have formed from volcanic ash that every so often exploded from a volcano some distance away. The ash would have spread out in the atmosphere, then rained down here as the Lickey Quartzite was forming. The inset picture shows a present day volcano ejecting ash into the atmosphere. This ash can be carried thousands of kilometres by the winds. The clay formed from the deposition of the volcanic ash in sea water is called Bentonite.
Hills and Valleys
If you have been up onto the top of the Lickey Ridge, you know that it is a long, high hill. There is a beautiful view from the north end of the ridge towards Beacon Hill and a deep valley in between (photo above). The Lickey Ridge is made of hard quartzite rock and Beacon Hill is made of another hard rock from another period of deep time that we will encounter later. But why is the valley there? Touch the map in the area of the valley (near the golf course) to find out what kind of rock is there. The label Carboniferous Mudstone should appear at the foot of the map screen. Mudstone is a soft sedimentary rock, especially when compared with the Lickey Quartzite and the other hard rocks of Beacon Hill. So when erosion gets to work, which will be worn away most? Erosion of the mudstone is only part of the story though – see the following screens.
Sedimentary rocks are one of the three main rock types that we find on Earth.
IGNEOUS rocks are crystalline rocks that form when hot molten material (magma) erupts from the interior of the Earth and cools and solidifies. We will see some of these later on our voyage. Granite and basalt are well known examples of igneous rocks.
SEDIMENTARY rocks form when layer upon layer of sediment (the eroded fragments of other rocks) are deposited, often on the bed of a river, lake or sea or in the dunes of a desert. The weight of the layers of sediment above compresses that below into rock. Sandstone and mudstone are sedimentary rocks. There is one other way that a special kind of sedimentary rock forms in the sea. Limestone is a sedimentary rock made up of the broken or dissolved remains of shelly sea creatures that have died and fallen to the sea floor. Layers build up and are cemented together by the mineral calcite, which is what the shells of sea creatures are made of.
METAMORPHIC rocks form when other types of rock (igneous or sedimentary) are altered by intense heat and/or pressure as they are squeezed or buried deep in the Earth by the movement of tectonic plates, or heated because of the presence of very hot magma. The minerals in the original rock are changed chemically and the physical structure and appearance of the rock may alter. Metamorphic rocks often have interesting swirling textures or a beautiful lustrous appearance.\n\n The names of some metamorphic rocks may be quite familiar to you, such as slate (which is altered mudstone) and marble (which was originally limestone). Others have less well-known names, such as gneiss or schist.
From sandy beach to rocky hill
When sediment is first laid down on a sea bed, the beds are usually close to horizontal – but the rock beds in the quarry dip steeply towards you. Something dramatic has clearly happened! At depth in the Earth it is hotter, so rock is more flexible when it is deeply buried. At a time when these beds were buried they were compressed by massive earth movements which caused the rock beds to buckle and fold. The Lickey Quartzite was folded upwards into an arch shape called an anticline. Sometimes, when pressure is applied to rocks which can cause them to fold, they may fracture as well and slip along a flat surface that we call a ‘fault’. The diagram above shows a fault either side of the Lickey Ridge (the brown dashed lines). You can see how the rock layers have slide down on either side of the ridge of Lickey Quartzite. Erosion over millions of years has removed much of the folded rocks, leaving behind the hard core of the Lickey Quartzite forming the ridge.
Earth movements on this scale are caused by the movement of tectonic plates – the enormous slabs of rock that cover the Earth’s surface and on which the land of the continents is carried. The plates move very slowly (about as fast as your finger nails grow) but over millions of years they can carry the continents a long way! When two tectonic plates collide, the pressure is so great that horizontal beds of rock are squeezed until they buckle and fold and the effect can be seen over very large areas, even hundreds of kilometres away. This is what has happened to the Lickey beds. Collisions like this push the rocks up to form big mountain ranges.
In Ordovician times, the land that is now England was part of a small continent called Avalonia. An ocean called Iapetus was to the north. Over millions of years Avalonia drifted northwards as the Iapetus Ocean closed and eventually collided with a big continent called Laurentia. This is the collision that caused the folding of the Lickey Quartzite. You can learn more about this in the Lickey Ridge Voyage.
Erosion by ice
It is thought that the softer Carboniferous mudstones we see now in the base of the valley, and other soft rocks to the east of the Lickey Hills, were eroded away further by ice during the last ice age, about 25,000 years ago. The ice had much less effect on the hard Lickey Quartzite, and the upwardly folded and faulted rocks were left exposed as the high Lickey ridge after the ice had gone. The picture illustrates how the area may have looked as the ice was retreating. The Lickey Hills ridge, still covered in ice and snow, is surrounded by a plain of pools, lakes, river channels and stones left by the melting ice.
There is just one place where erosion has cut through the hard Lickey Quartzite. A few hundred metres north of where you are standing, there is a deep gash in the Lickey ridge, which we call the Lickey Gorge, where the Rose Hill road now runs west-east through the ridge.
Cutting the gorge
One theory about the Lickey Gorge is that it was formed by massive torrents of water overflowing eastwards from a lake of glacial meltwater, dammed west of the Lickey ridge, towards the end of the last ice age around 18,000 years ago. Meltwater rivers carry huge volumes of water from melting glaciers and have tremendous erosive power – far more than any river we have in Britain today. Although this sounds convincing, no evidence of a dam or debris from it has been found as yet.
The danger in the gorge today is vehicles, but 18,000 years ago, the gorge may have looked very different filled with torrents of ice cold water. It must have been a sight to behold, and very noisy. The picture of glacial meltwater in Iceland shows that a large volume of fast moving water can cut a substantial gorge through even the toughest rocks (basalt in this example).
Follow the fault into the gorge
As you continue on the track down towards the main road, you will be walking along the line of the big fault that runs down the western side of the Lickey Ridge. On the east side (right hand side) are the 480 million year old Lickey Quartzite rocks. On the west (left hand side) are the 305 million year old Carboniferous Mudstones. The fault is shown as a definite line, but in practice, it will be a zone, perhaps several metres wide, of shattered, crushed rock. The app will say ‘Environment Change’ often as the path takes you from one side of the fault to the other and therefore back and forth between the environments of the Carboniferous Mudstone and the Lickey Quartzite. At the end of the track you cross the Lickey Gorge and the very busy Rose Hill road. Cross this road with CARE.
The reference to ‘monsters of the Anthropocene’ (on the map) is a reference to the vehicles on the road. The Anthropocene is the name that has been proposed for the geological time period we are currently living in.
Task Site 2 Questions
The rock bed surface in the quarry shows ripple marks because the sediments were laid down in:
a) In a big river
b) In desert sand dunes
c) Under the waves of a shallow sea
d) In a lake while the wind was blowing
There is low ground between the Lickey Ridge and Beacon Hill mainly because:
a) People blasted out the valley to make the road
b) An earthquake caused the ground to subside
c) There is a softer rock in the valley
Touch the clock to find out what the oxygen levels in the atmosphere were like in the Ordovician:
a) 5 to 6%
b) 18 to 19%
c) 25 to 30%
d) Over 40%