- When a print or impression of a plant or animal is covered over by sediments, which gradually form rock around it.
- When a plant or animal is caught in something that hardens around it - like amber, ice, tar or a peat bog - and preserves it.
- From objects like shells or bones, which are covered by sediments and then are slowly replaced by minerals.
The fossils pictured here are all 'coal measures' fossils, which means that they were found deep down in the earth by miners working at coal seams. They are all made from plants and trees which grew over 300 million years ago.