Trowbarrow LNR is owned by Lancaster City Council and managed by Arnside & Silverdale AONB. Please be aware that you enter the disused quarry at your own risk as there are many hazards associated with the site, such as high rock-faces, loose and potential falling rock, falling tree branches in high-winds, and rough surfaces. The site is accessible for quiet recreational access via the gates, please read the notices at the entrances. The site will have tree-felling and woodland management operations going on from time-to-time, so these activities and areas must be avoided as per warning notices when work is being undertaken.
The site is a geological Site of Special Scientific Interest (SSSI) and damage and disturbance of rocks and fossils is prohibited; no geological hammers or digging is allowed under the SSSI notification.
A very important health and safety aspect is the potential serious hazard of the intrinsically fragile and unstable nature of the high rock-faces. Anyone climbing here does so at their own risk.
Please keep away from the base of the main climbing areas in case of rock fall.
Trowbarrow is a great site to explore. Park at the suggested waypoint. Go up the steps into the wood, take the left hand path and follow through to a signpost, turn north along The Trough to waypoint 1 - the first of our three sites.
The rock forming Trowbarrow is limestone. It's composed of fragments of the shells and skeletons of corals, algae, shellfish and plankton, which accumulated on a seabed. The resulting calcareous sands were transformed into a rock by the deposition of calcium carbonate in the pore spaces between the grains. It was formed about 340 million years ago during the Carboniferous geological age.
The rock built up layer by layer into beds with muddier thin layers between as conditions changed - called bedding planes. In most of the quarry the beds have been squashed, bent and tilted into a vertical position. A monoclinal fold is the technical term here!
There are different types of limestone, formed under slightly different conditions. Youngest and forming the main quarry is Urswick Limestone. At times, probably when sea levels fell, it was exposed at the surface thus allowing rain to cement the particles together with calcite and form a hard, dense rock which is resistant to weathering. It must have been harder to quarry but was better quality chemically.
Older is Park Limestone - formed in deeper water and never exposed at the surface so the grains weren't 'cemented'. It is comparatively weak and weathers to rubble and scree, often forming gentler slopes in the landscape.
A third main rock type forms a layer within the Urswick Limestone, splitting it into upper and lower sections. Over time, changes in climate, sea level and crustal movements led to muddy water flowing into the sea and building thick layers of mud. This became a distinct layer of mudstone called Woodbine Shale, found over a large area of South Lakes. Fossils can still be found in it, which suggests the mud arrived in short pulses which didn’t destroy all the fauna of the clear water. Over thousands of years a large layer built up, which today forms The Trough running across the western side of Trowbarrow. The layers have been tilted vertically and the mudstone has been eroded leaving a straight, deep trough with sheer walls of limestone.
Site 1: The Trough Follow the path in the bottom of the Trough. The Woodbine Shale isn't obvious on the floor, probably some limestone infilling to make a track, but there are a few lumps of mudstone here and there. See if you can spot some rocks that aren't limestone. Two questions to answer at waypoint 1.
Question 1: Assuming a rate of deposition of 0.5m per thousand years, how many years did it take to build the layer of Woodbine Shale? (Hint - measure the width!)
Question 2: Standing in the Trough, looking at the high walls on either side, which rock do you think is harder - the WBS or the Urswick Limestone? Any ideas why?
Onto waypoint 2 and the fossils. Continue up the Trough and through the memorial gate. Lots of blocks further on! Follow the path as it curves east out of the trees into the quarry. Head for waypoint 2.
Site 2: Fossils To the east of one of the entrances is a rock wall with numerous fossils of two main types. The circular formations are fossilised corals. The other type are cylindrical stick fossils. These are not the remains OF creatures but remains of their activity. They burrowed in and ate the sediment and excreted the inedible parts - yes, it's a sort of fossilised 'poo'! Because these are not fossils of actual creatures they are called 'trace fossils', in the same way animal tracks or footprints would be.
Question 3: What sort of seas do you think existed at the time the corals and burrowing creatures existed? (Hint - think about corals that exist today)
Question 4: Measure the coral fossils - what's an average diameter?
Question 5: How many corals can you see on the wall?
Question 6: Looking at the fossil covered seabed here - can you suggest some obvious changes that have happened to the layers of limestone since they were formed?
Head north along the quarry floor. On the left is the large Shelter Stone where the quarry men would hide before blasting happened. The impressive Main Wall on the east side of the quarry clearly shows the vertical beds of limestone and the cracks and joints making the face slightly unstable. Big piles of rubble at the base from earlier falls! The main wall surface is a famous example of a 'stick bed'.
Site 3: Red Wall
Head west into the trees and the third site at the foot of Red Wall, popular with climbers. They aren't climbing up a 'wall' however, but crawling across a 'pavement'! This was once a horizontal limestone pavement with soil and vegetation eroding the surface. This 'fossil' surface is called a 'paleokarst', with the red staining coming from the clays of the soil. The 'wall' is pock-marked with varrying circular and elliptical depressions and sinuous fissures.
Question 7: What do you think might have caused these 'holes' in the pavement? (Hint - look around you!)
You can continue to explore the quarry, plenty more to see, or head back - the shortest route is via the entrance near Site 2.
Please email your answers via my profile to claim your Earthcache find.
Developed with permission from Arnside & Silverdale AONB who manage the LNR and using information available from their website.