Fingle Bridge, situated in the lovely Fingle Woods, is a picturesque crossing point of the River Teign. From historical texts it appears that there was no bridge at this location before the 1600's. There is a record stating that in the year 1665 the bridge crossing at that point was "in decay". Obvious in between then and now the bridge was repaired or rebuilt. The current bridge is clearly still a historic bridge, a number of factors highlight this. The more obvious are the recesses on the cut waters, which are designed to allow those crossing the bridge get out of the way of horses or carts, and the narrow width of the bridge, at only 7 feet. That makes Fingle Bridge one of the narrowest examples on Dartmoor. It is likely that the bridge was originally built to service industrial activities along the Teign Gorge. These include corn milling, charcoal burning, bark ripping and timber. All of these industries would have transported their produce by pack horse, meaning the bridge didn't need to be wide.
The bridge and woods are named after the stream which has its confluence (meeting point) with the River Teign here. The Fingle Stream rises near Whiddon Down and then flows down towards the valley. The word 'Fingle' has multiple possible meanings from Old English. The possible derivations are 'Fang', 'Fengle' and 'Fengelãd'. The first word 'Fang' has two possible definitions, the first is to 'hold' or 'catch' and the second is 'plunder' or 'bounty'. The second word 'Fengle' means 'prince' or 'king'. The third word 'Fengelãd' means 'marsh path' or 'fen'. The earliest record of the place name was in 1317 and the earliest mention of Fingle Bridge in the Duchy of Cornwall records is dated 1755.
As well as being a beautiful and peaceful location, at least on days where there aren't too many people enjoying either the beer garden or the river in nice weather, the area is also interesting from a geological and fluvial geomorphological point of view, hence this EarthCache. Although the latter of these sounds really impressive, and daunting, the actual study can be simply summed up. Fluvial geomorphology is the study of water and sediment movement in river catchments and channels and their floodplains. As already mentioned at Fingle Bridge there is the confluence (meaning joining) of the River Teign and the Fingle Stream, just down stream from the bridge. The reason that this confluence is interesting for the study of geology and fluvial geomorphology is that both rivers rise, and have their courses, over different geological units and soils. At Fingle Bridge this is obvious, even with a cursory glance, as the meeting of the waters from the two water course have different colours and suspended sediments making for an interesting, and visually impressive, fluvial geomorphological feature.
At the posted coordinates you will find two water courses. The larger one, that flows underneath Fingle Bridge and down the impressive Teign Gorge, is the River Teign. The smaller one, joining the River Teign from the north (pub side) is the Fingle Stream.
The River Teign rises on Dartmoor and actually has two sources, one at the Teign Head and the second near Grey Wethers. Teign Head forms the North Teign, which flows generally north east before meeting the South Teign. The South Teign rises near Grey Wethers before flowing through Fernworthy Forest and the Fernworthy Reservoir. From there it flows north before meeting the North Teign at Leigh Bridge. After the meeting of the two branches of the Teign the river flows roughly north east before entering the Teign Gorge, just south of Castle Drogo. The dramatic change of topography of the river flows through is linked to the change in geology. Prior to the river entering this deep steep sided valley south of Castle Drogo the course of the River Teign, and all of its catchment, is on Granite bedrock and the acidic soils associated with this geological unit. These soils include the superficial geological unit of peat. After entering the Teign Gorge, which is a result of the change to a softer geological unit compared to the Granite, the River Teign flows over mudstones and metamudstones of the Crackington Formation. These mudstone and metamudstones is the bedrock at the posted coordinates.
The Fingle Stream rises just to the east of Whiddon Down, flowing almost due east until it turns course south to join the River Teign at Fingle Bridge. Unlike the River Teign, which has its course over two geological units before this point, the Fingle Stream only flows over one. The sole geology that the mudstones and metamudstones of the Crackington Formation.
As water flows over and through a geological unit, either in the form of surface water or within a water course, the water interacts with it. This results in units of rock being slowly eroded, and units such as peat, having minerals leached from them. Peat, not being a rock, but a form of compressed organic material, doesn't react in the same way as the granite beneath it. On Dartmoor when water flows through the peat there are some sediments picked up by the water, but these are often quickly deposited, meaning that the largest affect on the appearance of the water, are the mineral iron and humic acid. These are both dissolved within the water and give Dartmoor water that characteristic reddish brown tinge.
Rocks too leach out specific minerals they contain, but they also affect the appearance of water in a different way. As rock is broken down by all forms of erosion, these smaller pieces of rock are washed into the water courses. The hardness and type of rock determines any visible affects that occur to the colour and clarity of the water. Granite, which is a hard rock containing lots of feldspar crystals, tends to break down to a mixture of pebbles and sand as the smallest fraction. As a result, unless a water course is in spate they either sit on the river bed, or are bounced or rolls along. As a result Granite does not commonly affect the colour or clarity of water flowing over it. Softer, or finer, rock types, such as mudstones and siltstones commonly erode down to a much smaller fraction. This is because, as their names suggests, the rocks are made up of compressed mud and silt respectively. Because the size of the eroded particles are much smaller than that of Granite, they will be help in suspension. This means that they affect both the clarity and colour of the water for the watercourses that flow over them.
To log this EarthCache please go to the posted coordinates and send me your answers either via email or through the Geocaching messenger. Although I have checked this location on a number of occasions to confirm that the visual effect shown here will be regularly observed, due to changes in conditions the levels of visibility may change. So if there is no obvious effect at the point that the Fingle Stream meets the River Teign then you may have to compare the water colours from within the water courses a little upstream on the respective water courses from the confluence.
1) Look at the water from both the River Teign and the Fingle Stream and describe their appearance (e.g. clarity, colour and any particles in suspension etc).
2) Where the waters from the two water courses meet describe the visual effect that this confluence creates
3) What is the main reason for the difference in appearance of the water from the two water courses?
4) Based on what you have seen here do you think that as more water courses join the River Teign, will the appearance of the river's water change with these additions?