stone crushing plants tend to fall into one of two types: stationary crushing plant and mobile crushing plant. Stationaray plant constructed upon permanent foundations tends to be associated with relatively larger reserves providing extended life (ideally 30 years or more for hard stones; ten years or so for sand and gravel) supplying a variety of markets in terms of aggregate type, tonnage and locations. The relatively short life of sand and gravel deposits means that the process plant may be removed and used again on a later development. 'Modular construction' of such plant, that is prior fabrication of units of the structure and installation of appropriate equipment, greatly facilitates both removal and rapid erection. 'Mobile' plants tend to be dedicated to major construction projects, such as airport runways, motorways, dams etc, the life of the operation and volume of the reserve being determined entirely by this single market. They may also be employed within a quarry to augment temporarily the capability and the capacity of a 'Stationaray' plant to satisfy a shortterm market or during the development stage.