a pair of floor plates 39 which form the floor sill of the roof support unit associated with that guide section a roof shield not shown is supported above the floor sill by means of hydraulic props 38 the cylinder of a hydraulic advance ram 43 is attached to the yoke 41 its piston rod 44 being connected by means of a link 45 to a transverse rod 46 which is coupled by links 47 to the two floor plates 39 thus the guide rods 21 can slide relative to the floor plates 39 in the direction of advance s fig1 shows the control apparatus in its normal position with the guide section being supported on the mine floor 13 by means of the end edge 12 of its slide plate 14 by extending the hydraulic control rams 28 the guide 10 is tilted into the position shown in fig2 here the end edges 12 of the slide plates 14 are lifted clear of the mine floor 13 and the guide 10 rests on the mine floor by means of its brackets 30 in this position the 34 climbing 34 position the plough will make a cut at an elevated horizon similarly if the hydraulic advance rams 28 are retracted the.