The Essex Rock and Mineral Society are currently conducting a survey into the types of rock etc. used in the construction of walls, with special emphasis on church construction.
Blocks and cobbles of building material dug from nearby pits, cleared from the land or transported up rivers from seashores, have long been used in the construction of thousands of walls in the region, especially church walls.
Materials used in churches and walls in and around Essex may thus broadly reflect underlying geology and river transport.
These materials could therefore provide some access to geology otherwise hidden beneath the landscape.
The question is how good a reflection is this? Is there a pattern to wall building that reflects the underlying geology in any meaningful way? Does the pattern also reflect a configuration of transportation of materials from the coast and from outside the area?
This project should enable us to test whether there are any such patterns.
Church and tower walls, garden and cottage walls and estate walls all provide evidence.
Flint frequently forms the majority material in Essex cobble walls. Flint is extremely variable in size, colour, texture and shape. By far the best way to ‘get your eye in’ is to view as many different verified flints as possible. Flints that have been quarried from Chalk are very often black inside with a white surface; they may be either whole or broken. Some flints were carefully broken or ‘knapped’. Skilled knapping produced beautifully shaped blocks, squares and special shapes in flint for some walls. Many flints from gravel and glacial till deposits are stained brown to red internally with iron minerals. Some are brown, grey or black on the outside or quite mottled. Many are in strange shapes; some have holes in or through them. Red and pink flints, usually crackled, have been heated in fires. Flint pebbles and cobbles were rounded on ancient seashores and incorporated into gravel deposits. If possible, note the proportions of flints used as cobbles (naturally-worn), ‘raw’ nodules (unworn, as they came from the Chalk), or ‘knapped’ (split or shaped artificially). Flint frequently forms the largest proportion of a cobble wall.
Many flints are broken: look very closely at any breaks and observe characteristic conchoidal (shell-like) and curved fracture surfaces, a bit like broken bottle glass. These are characteristic of flint.
Flint pebbles frequently show 'chatter marks' on their surfaces: fine, slightly curved indentations into the pebble surface which look as though a fingernail has been pressed in. These marks are characteristic of flint and help to distinguish flint from the other common materials in the walls.
Other rocks which may occur include vein quartz, quartzite, puddingstone, cementstone, limestone and ferricrete. Roman brick acan also be found in the construction of churches, which indicates the presence of a roman site in the vicinity,
Visit the Essex Rock and Mineral Society website for a more details.