Photograph courtesy of National Museum of Wales

​

This is an example of pit propping. Here the rock strata which forms the roof is being supported by wooden pit props, with a flat being used to act as a lid type timber to support the roof. A flat was a round timber cut down length-wise in two pieces and was used for many different jobs underground apart from the one in this photograph. The nice flat edge would be ideal for making the sleepers, for supporting the tram rails underground. Flats were used in a crisscross fashion to build up in a recess (hole in the roof) after a fall. It was essential that any roof supports on the coal face were near vertical, for any sudden weight on a prop that was not upright could cause either the top or bottom of the prop to kick out with possible devastating results.