Abstract: A mechanism for cutting hard earth formations such as rock comprises a prime mover vehicle such as a crawler tractor having a back plate fixed thereto. An elongated cutter bar framework is secured to the back plate in pivotal manner by means of a tool bar structure that is pivoted directly to the back plate. A motor mechanism such as a linear fluid motor is interconnected between the tool bar and the vehicle structure and is controllably operative for establishing particular angular relationships of the cutter bar framework relative to the formation to be cut and having the effect of controlling the depth of the cut being made.