Welcome to Burgh Castle!
This is an EarthCache which means that there is nothing physical to find at this location. Instead, visit the section of wall at the coordinates and answer the questions below. Please send your answers to me by email or via the Message Centre. Once you have sent your answers, you can log straight away – I will contact you if there are any issues.
Questions:
1. Look at the flint in the wall, to the left of the tower. Describe the features of the stone (e.g. colour, shape and size). Are the stones arranged in any particular pattern? Why do you think this is?
2. Now look at the flint and its formation, in the tower to your right. Does the flint in the tower look the same as the flint contained within the main wall? Why might this be?
3. Please upload a photo of yourself or a personal item with the ruined wall in the background.
Flint:
Flint is a sedimentary form of mineral quartz, categorised as the variety of chert, that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires. Flint breaks and chips into sharp-edged pieces, making it useful in constructing a variety of cutting tools, such as knife blades and scrapers. The use of flint to make stone tools dates back more than three million years. Flint’s extreme durability has made it possible to accurately date its use over this time.
“Flint knapping” is the name given to the process of chipping the flint into the required shape using a “hammer stone” which needs to be harder than the flint itself. Otherwise, the hammer stone will break during the process.
Flint is formed as a result of a chemical reaction within the host stone. It is considered to have begun forming soon after the deposition of chalk. Silica within the flint replaces the original chalk, grain by grain, effectively taking its place. Chalk is an alkaline rock so acid has to be generated to dissolve the chalk. This is so the silica can take its place. Bacterial activity from sediment in the sea bed generate hydrogen sulphide and when this meets oxygen, acidic conditions are generated. The silica that forms the flint comes from silica fixed in the skeletal structure of marine organisms.
Flint comes in a range of colours, due to impurities in the rock. It is harder than the surrounding “host” stone it is found within and so it can sometimes be mistaken for a fossil. As flint is a sedimentary rock, fossils do sometimes exist within the stone. These are usually sea-life creatures such as sea urchins or small shellfish.
Weathering:
There are three main types of weathering. These are biological, chemical and physical.
Biological weathering is caused by movement, from plants, animals and humans. For example, a new tree may grow larger and as it does so, its roots cause various existing cracks to widen. Over time, this wears down rock. Lichen also produce chemicals which help break down the rock, so they can get the nutrients they need.
Chemical weathering is caused by the various chemicals that can be found in rainwater. Rainwater is slightly acidic (due to carbon dioxide) and so when it comes into contact with rocks, a chemical reaction can occur, which causes weathering.
Finally, physical weathering happens due to various Earth processes, such as wind and rain. One of the most common types of physical weathering is known as freeze-thaw, which is when rain water fills a crack. If the temperature suddenly drops, the water freezes, expands and makes the cracks/holes in the rock larger. This can keep happening over time, making the cracks/holes bigger and bigger.
This cache has been placed with the kind permission and in collaboration with the Norfolk Archaeological Trust.