The land around this EarthCache, and the village of Sampford Peverell, is full of history. The first mention, and the origins, of a settlement at the site appear around a road linking Tiverton with Wellington, where the road crossed the river. The land was held by a thane or fuedal lord, and was recorded in a Saxon estate charter dated 958 AD. The village was also recorded in the Domesday Book and was called as "Sanforda". This, as the modern name, is probably a reference to a river crossing at a sandy ford. Here is the first way that the local geology has a visible impact on the area. The second and equally important is the later industrial activity in the 18th century. Several quarries were set up, including one at the site of this EarthCache. Both the quarrying, and the very name "Sampford", are direct results of the underlying geology of the area. This is a sedimentary rock called Breccia, and is more specifically part of the Sampford Peverell Member of Breccia. This is Permian in age and is part of the Halberton Breccia Formation, which in turn is part of the Exeter Group of Breccias.
Breccias can be formed in a number of different ways, but those found in Devon are mainly a sedimentary rock. The vast majority of Devonian Breccias, which there are many local types, are a cemented sandy matrix containing fragments of other types of rock within them. Breccias are formed by similar processes to Conglomerates, which Puddingstone is a well known example of. However, the difference between Breccia and Conglomerates is the shape of the rocks included within the finer material. In Conglomerates these are usually well rounded, either through riverine or sea processes, where the inclusions in Breccias are far more angular, as they have had less time to be worn and rounded. Breccias form where you get sedimentary rocks being laid down with mainly relatively fine material, such as sand, and then to this fragments of other types of rock, both local and non local, are deposited within the finer material.
Because these larger inclusions can vary in type of the parent rock, age since separated from the main body of parent rock, and the processes of erosion they are subjected to, a single type of Breccia can have a range of inclusions that in some cases can indicate the source and 'history' of the material. As already said there are a number of factors that affect the shape of the inclusions within Breccias, but as a rough guide Breccias that form with younger material, such as those formed at the base of cliffs, will tend to have more angular inclusions, to those that are formed at greater distances to the source of the parent rock.
Geologists often have reason to classify the subjective roundness of sediments or rocks and this is commonly done by categorising them into very angular, angular, subangular, subrounded, rounded or well rounded. This is show in the Figure 1 to help demonstrate what each of these categories looks like.
Figure 1) The common categories of roundness
The large variations in different types of Breccias means that they have varying properties, such as resistance to weathering. The less well cemented a Breccia is, the weaker the Breccia will be. Despite many Breccias being poorly cemented, and therefore relatively susceptible to erosion, it is commonly used a local building material in areas where Breccia is found. Sampford Peverell is no exception. On the way to this EarthCache, if you approach from the suggested trailhead, look at the garden wall to you right as this wall is made from the local Breccia. Many of the buildings within Sampford Peverell also have parts using Breccia. Most of these show extensive signs of erosion.
To log this EarthCache please go to the posted coordinates and Stage 2 and send me your answers either via email or through the Geocaching messenger
Posted coordinates
1) Describe the makeup of the Breccia at roughly eye level, from the finer material to the larger inclusions.
2) Looking at the overall rock face. Would you say that this is one homogeneous/uniform rock that has little or no variation, or can you see definite layers of subtly different makeup?
Go to Stage 2
3) Looking at the Breccia here would you say that overall the inclusions are very angular, angular, subangular, subrounded, rounded or well rounded?
4) Based on what you can see would you conclude that the inlusions were relatively close to the parent rock, or at a greater distance?