Gollinrod Gorge is a hidden place, out of sight to all but locals and those in the know. It is where the Irwell develops a roar and a rush as it rusn through a narrow cliff lined gorge. The geology around here is mostly from the Carboniferous period. The Carboniferous Period lasted from about 359.2 to 299 million years ago, and the rocks that lie underneath the valleys and hills of Rossendale were formed millions of years ago at a time when the whole of what is now the North of England was covered by huge river deltas and lagoons. Sediments, mainly sands, silts and muds, were eroded from hills in an area that now includes Scandinavia and Greenland and were swept into vast river deltas and lagoons in a central basin in a position now occupied by the Pennines. The sediment settled to the bottom as the water slowed down in the deltas and lagoons. The nearest equivalent sediments of today are forming in huge river deltas such as the Mississippi delta.
The co-ordinates of the earth cache take you to an area of rocks and sandy beach at the side of the River Irwell, it is here that the river turns into the narrow gorge beneath an impressive cliff. All around are a number of rocks of different sizes, shapes and feel, some rough, some smooth. There is also evidence of the human past at times with broken water worn crockery and glass, if you are lucky you may find some with lettering on it.
You will notice some darker stones, black and blacky grey, these are known as mudstone. Mudstone is a fine-grained sedimentary rock. It is usually black or dark grey-brown and is often soft and crumbly. Mudstones form when very fine-grained clay particles are deposited in water. They tiny particles settle to the bottom of oceans, lake floors or lagoons or even in quiet stretches of rivers. As the mud is buried and compacted by overlying sediment, the water is squeezed out and it turns into mudstone. You will notice that some of these rocks have lines on them, these lines are evidence of sedimentation, which the natural process in which material (such as stones and sand) is carried to the bottom of a body of water and forms a solid layer. Some of the layers are thicker than others, though with mudstone they tend to be very thin. Now why have I brought you here? Do you want a lecture about mudstone, or a view into the past. For this you will need your eyes, and perhaps a blunt knife. Find a piece of mudstone and carefully seperate the layers, you may notice evidence of plant fossils, which around here tend to be grass and reed fossils. They are extremely thin and delicate.
So this being an earthcache there are some tasks to do:
1. Please describe the mudstone in terms of how it feels, what colour it is and how thin are the layers of strata.
2. Please describe the fossil plant that you find.
3. Please find evidence of erossion by the river on the pieces of mudstone, and explain why you think the river has caused it.
Please email me the answers, do not include them in your log. This earthcache is not intended as a test or exam, but more an exploration of the awareness of what can be found in the local geology.
Now please be careful, the river can rise and run very fast. If you do not think it is safe, do not approach the site. You need to be on the western bank near the green pipe to be in the correct area. It is also rough underfoot.