1 the structure 3 is associated with a boom type control arrangement usable to control the cutting horizon of the plough this control arrangement has boom or jib like guide linkages 9 with resilient bars or beams and each of which is formed as a flat platform or rail 11 at least over a region which bridges the goal access zone 10 of the working and carries an upwardly projecting rigid headpiece 12 each linkage 9 11 constitutes part of the walking or shifting mechanism not shown which enables roof supports and the conveyor 1 to be displaced in alternate walking steps towards the mineral face each linkage 9 11 is guided for displacement in the shifting direction of the roof supports as well as to pivot in a plane at right angles to the mineral face the linkages 9 11 thus performs a boom or jib control function as well as guiding the supports and transmitting the shifting forces so that the conveyor 1 and the plough guided on it is supported and controlled in the known manner as for example described in u s pat no 3 915 500 and as represented in fig4 to 6 as represented by the arrows in fig2 associated with each guide linkage 9 11 there is a slidable guide member or piece 13 which is mounted on a fixed cover component 8 so it can be raised or lowered the member 13 is a narrow plate or strip with a width smaller than its length i e height a plane rear face of the member 13 is slidably engaged on a plane outer support face of the cover component 8 which is rigidly mounted to the associated conveyor channel section the member 13 is.