Mining layer is a term used to describe a LEDGE or shelf of rock that is found in a mine. It is typically a horizontal layer of ore or mineral deposits that are found in the walls or floors of a mine. The term 'LEDGE' is used to describe this layer, as it is usually a flat surface that can be easily accessed and mined. Mining layers are important for miners, as they provide access to valuable resources that can be extracted from the mine.