has on its distal end a cutting head 14 for drilling borehole 15 as is conventional a drilling mud is supplied to the drill pipe string 13 from a mud pump 19 the drilling mud supplied to drill string 13 exits the drill string at the distal end thereof adjacent the cutting head 14 and is flushed to the surface of borehole 15 along the path indicated by the arrows in fig1 the drilling mud which returns from the borehole 15 and which contains drill cuttings is supplied to a series of shale shakers 31 also called main shakers which separate the drill cuttings from the mud a mud pit 33 is provided below the shale shakers 31 to receive the mud separated from the returning mud and cuttings mixture the returned mud is then recycled from the mud pit 33 and supplied to suction pit 21 for subsequent reuse in accordance with the method described in the above referenced application artificial drill cuttings are added to the drilling mud by means of an artificial cuttings feeder 27 the artificial cuttings are supplied into a chute 23 which also may receive fresh mud from mud supply 25 and provides this to the input of mud pump 19 as a consequence the returning drilling mud passing through mud return conduit 29 and into the shale shakers 31 contains a mixture of both artificial cuttings added by feeder 27 to the drilling mud and natural drill cuttings generated by the rotation of cutting head 14 in the borehole this cuttings mixture 35 is in accordance with the invention supplied to a mini shaker.