The Yorkshire Dales

In 1954 a large chunk of Yorkshire (now Cumbria) was sectioned off to produce the Yorkshire Dales National Park. The National Park today is visited by millions of visitors and farmed on by hundreds of farmers, however over the preceeding millenia this area has been affected and changed by a large number of factors, some of which have been introduced below.

The vast majority of the Yorkshire Dales landscape is dominated by limestone from the Carboniferous, which on the higher fells is typically capped by Millstone Grit. A look at a geological map of the area shows, however, a slight discrepency in the North East of the region – instead of the typical limestones, a large number of mudstones and sandstones can be found. These are Silurian in age, and have been brought up level with the Carboniferous limestones by the large Dent Fault.

Geological Map of Yorkshire Dales (From BGS Geology of Britain Viewer)

The different rock composition here reflects the changing depositional environments this land mass has experienced. For instance, the Silurian mudstones and sandstones suggest a relatively deep sea environment, which was unable to carry much sediment. This meant that only fine grained particles were able to be entrained and deposited, producing the mudstones. The fauna in this mudstone can vary from being purely composed of graptolites and planktonic organisms which suggests that the lower reaches were predominantely anoxic, to regions where burrows can be found which imply oxygenated soils. This reflects the variation in sea level during the Silurian and Ordovician time, likely related to the Ordovician glaciation.

Location of continents during Silurian. (USGS)

On the other hand, the Limestone of the Carboniferous, almost a hundred million years later, suggests far warmer, shallower seas in a tropical climate. Corals, trilobites, crinoids, and brachiopods can all be found in these rocks which suggest that it was a very well occupied environment. Younger rocks atop these often can be found to contain sandstones and coals from coastal swamps of giant ferns.

Continents during Carboniferous (USGS)

The variation in the rocks across the Dent Fault also has an impact on the geomorphology of the landscape. In the Silurian mudstone bedded environments, the hills tend to be taller and steeper – this is related to how the mudstone is less able to be eroded by acid rains and other flows. The basic limestone reacts with acid rain (as is used by geologists to test for them!) and so over thousands of years they have been chemically eroded. As bogs tend to occur where there is water at the ground surface, nutrients are scarce and the ground surface is acidic these tend to be found predominantely in mudstone areas, which helps to obscure these outcrops from view.

In the Carboniferous areas there is often a large amount of exposed outcrop. Shake holes can often be seen, generally as a result of collapsed caves; The karstic limestone often forms subterranean caves and underground rivers (aiding its drainage ability) which are susceptible to collapse.

This variation in underlying bedrock in this area is very well demonstrated around Taythes Gill. Here, as you traverse east to west along the Gill you start off in fine grained muddy sediments, which all appear to be dipping in a general westerly direction. The quality of this mudrock decreases as you reach the fault zone, after which the carboniferous limestone can be found. Close to the edge this is often found modified to dolomite (the damage done to both sides around the Dent fault is likely related to the extent of movement across this boundary). Beyond this, the limestone appears to still be dipping west but it gets less steep as you progress along. This can be related to the motion of the fault, as demonstrated in a sketch below.

Taythes Gill geological map (from BGS Geology of Britain viewer)
Simple schematic showing an interpretation of the faulting in Taythes Gill

In addition to the large Dent fault, a number of smaller folding and faulting incidents have taken place and been kept in the geological record. For example, along the stream from Taythes Gill there is a large well exposed anticline, and in the Fell End Clouds there is another large anticline. The effect these folds and faults can have on the economic viability can be seen both in the Fell End Clouds, and in the Caldew Valley (Which is actually in the Lake District, but is very similar – in simple terms there has been a granite intrusion and post dated faulting, leading to veins).

Taythes Gill Limestone Anticline
Fell End clouds fold

When rocks fold or fault, they can crack. These weaknesses can then be filled under pressure by minerals, leading to features such as quartz veins, or calcite veins.

Cracked limestone with calcite veins.

These veins can contain a range of different mineral ores depending on their location and the chemicals around, which can then in some cases be extracted and processed to access the minerals themselves. In the Fell End clouds, for example, there is an old mine near to a large fold where the minerals malachite, azurite (both of which suggest the presence of usable copper ores), and galena can be found. Additionally, a lime kiln is present for decomposing limestone into quicklime. When this mine was in use during the Roman times, they could’ve potentially mined lead and copper.

This area has also been mined for its relatively accessible mineral supplies more recently. In the Lake District in Caldew Valley, there lies the Carrock Mine where ores of tungsten such as wolfram and scheelite have been mined. Mining was only thought viable here in certain instances – such as during both World Wars and the Korean War, when tungsten supplies were threatened.

Almost all rocks present are ancient – yet this is still a changing landscape. An ice age occurred ~16,000 years ago during the Pleistocene and the effects of this can be read in the landscape in certain places in the Dales where glaciations occurred.

Cautley Holme Beck. Red shows the scree, purple shows hummocky bedding and drumlins. Dark blue shows current current flow, light blue shows potential paleo current.
View from Cautley Waterfall. Purple shows bracken, pink shows drumlins, red line shows potential limit of glacier.

In the Cautley Holme Beck, a glaciation occurred. From reading the landscape, it is likely that the glacier started in the top area of the hill (the left most purple on the first image, with hummocky bedding; This is to the far right of the second image.). It then crept down through the valley, towards Low Haygarth, scraping the ground as it moved. It likely advanced only to the red line, which we can infer because this is where the bracken ends; Bracken prefers well drained soil, and after the glacier melts and retreats the escaping water would likely have created drainage paths throughout, allowing bracken to grow. As it retreated, collected rocks and debris within the ice were dumped out forming drumlins of till (as seen in the second photo), and later hummocky bedding around where the glaciation began.

The retreat of the glacier likely also meant that outcrop was exposed unsupported on the base. Once it was gone, this rock fell to produce scree slopes – hence, these scree slopes are only found on the outside path of the glacier and not on the inside.

The glacier, and others, potentially also affected the path of the feeder river. Originally this likely came through the far shallower V shaped valley heading to the north, however this now has very little water flow, with a waterfall  instead forming. The presence of a waterfall in this area like this suggests it is a new feature which has not eroded properly, which supports this hypothesis.

Cautley Falls

Once the glaciers had retreated the area was able to be colonized by humans. In one area, Victoria Cave has been foundd which contains an 11,000 year old harpoon point in a reindeer skeleton suggesting people have lived in the area for at least this long. Since that time a lot has changed.

Farming has taken a massive hold of the area. This has almost completely transformed the fauna and flora in the area, as without the millenia of farming that have occurred it would likely be covered almost entirely by woodland. Farming has driven grey wolves out from the area, which are now extinct here, while bear baiting has removed bears from Britain. This story is repeated again and again, so that todays Yorkshire Dales are almost entirely grass, bog, bracken and sheep.

Even today this sort of activity continues. Up until 2005 fox hunting was legal, and in some places this still occurs; When we visited the Yorkshire Dales on a mapping project, we saw a fox chased by a large pack of dogs through trees. Unfortunately, as we found out, the police in the area are unwilling to do anything without video or photo containing both the fox and the dogs – which is understandably needed as evidence, yet disappointing (to be clear, I have no issue with the police’s requirement for this).

Nowadays, the Yorkshire Dales are a point of pride for the beauty they present. The landscape is akin to a book, just waiting to be read. Millions of tourists visit the area year on year to go walking, hiking, running and mountain biking, and it is likely this will continue.

Published by

Ben

When I was younger I enjoyed reading books and watching shows about science, such as Nick Lane's The Vital Question and Chris Hadfield's Astronaut's Guide to Life on Earth. Since then, I've started a degree in Natural Science at the University of Cambridge where I'm specialising in Earth Science.

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