But despite the reason for it being dug, it is without doubt the most pristine sandstone outcrop in all the city. One of the hidden gems in all the sandstone outcrops in and around Nottingham must be Park Tunnel a tunnel originally made for horse-drawn carriages that was allegedly too steep to safely use. It’s well worth a visit to Castle Rock and spotting all the beautiful, curved layers in the cliff is a good way to spend time on a sunny day, especially given ample provisions for sustenance on the doorstep. You’ll see that other pebbles often stand out from the sandstone walls and cliffs but that the mudstone pebbles are often recessed, which is down to the mudstone being relatively soft and easily eroded. A quick trip into the famous Ye Olde Trip to Jerusalem pub and these pebbles can be seen with ease. The mudstone pebbles are actually very soft and are often smeared into weird shapes. ![]() The mudstone pebbles can in places be grey-green this is not their original colour but a colour change caused by water present in the ground. Some of these pebbles can be made of milky-white quartz, some are dark, almost black igneous pebbles, some are chocolate-brown mudstone pebbles. Some are small (coin sized) while others can be much larger (‘potato-sized’, as a guest on a geological tour once told me). PebblesĪlongside the crossbedding there are lots of pebbles scattered throughout the cliff. The difference in some of the sizes of these curved layers relates to the size of the original sandbar. If you look at satellite images (Google Earth is great for this!) of any of the big rivers in Bangladesh for example, you can see sand bars in almost every river channel and it’s very likely that our ancient Nottingham river looked very much like these. Some of you will be familiar with seeing sandbars or small ripples in rivers these are the same but much bigger! The technical name for these curved layers is ‘cross-bedding’. These layers are all curved: some look like interlocking U shapes while others exhibit more subtle curved lines, but they are all actually the same thing: examples of huge fossilised ripples that were flowing within the channel of the ancient river. These layers are interesting as they run contrary to the general thinking that sedimentary rocks are made of horizontal layers (like those you’d get in a good cake!) but if you spend even a couple of minutes looking at Castle Rock itself, it’s relatively difficult to see any horizontal layers in the cliff at all. But look closer and you’ll find all manner of subtle colour changes, from pale yellows to deep reds and oranges, and strange curved layers. Looking upon the approximately 30 m-high cliff you see yellowish rock. The evidence of this ancient river is recorded in the rocks we now see in places like Castle Rock. This river would have been very wide, likely thousands of metres, and it flowed over a barren, hot, desert-like landscape. This is because the sandstone was originally deposited by a huge river that flowed all the way from northern France some 250 million years ago during a geological period called the Triassic. This sandstone records a period of history that would have looked very different from our modern understanding of Nottingham. Castle Rock is made of the same sedimentary rock that is located directly beneath most of the city indeed it is this rock - part of a group called the Sherwood Sandstone Group - that hosts the myriad of tunnels and caves for which the city is also known. Despite this acclaim, the very foundation that the castle sits upon is often overlooked, by which I of course mean the rocky cliff of ‘Castle Rock’. Probably one of the most iconic sites in the city, Nottingham Castle is well known worldwide as the mythical centre of the fight between Robin Hood and the Sherriff of Nottingham. What are we doing about climate change?.Understanding carbon capture and storage. ![]() What causes the Earth’s climate to change?.NGR hydrocarbons (well samples) database.Palaeontology and biostratigraphy collections.Donations and loans of materials collections. ![]()
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