Abstract: A continuous miner has a pivotal boom mounting a rotor carrying picks for attaching and dislodging mineral deposit in a mineral deposit seam within host rock. A thin layer of mineral deposit is left respectively against a roof and against a floor. Ultrasonic sound waves are generated and are transmitted via a jet of water directed against the roof. Reflections are transmitted back via the jet of water to a receiver. Layers of the mineral deposit and the host rock are identified in respect of presence and location, by means of logic which generates a control signal to restrict pivoting of the boom to prevent cutting into the host rock by the rotor.