is continued to be pumped through the wash pipe 300 to pack the production screen 140 with the return fluid being routed through the lower production screen 140 the control mandrel 200 now is moved to the position illustrated in fig6 a 6b and 6c wherein the check valve 220 of the control mandrel 200 is now placed above the packer 100 and the series of seals 225 surrounding the check valve of the control mandrel 200 are in sealing engagement with the inner sealing surface 91 of the seal bore 90 the raising of the mandrel 200 obviously effects the closing of the port 111 of the lower sliding sleeve assembly 110 through the action of the shifting tool 240 on such sliding sleeve the port 261 of the cross over tool 260 is now positioned just above the open port 47 of the upper sliding sleeve assembly 40 the locating collet 250 is positioned just below the shoulder 52 of the seal bore 50 the seal rings 255 below the cross over tool 260 are in sealing engagement with the inner surface 51 of the seal bore 50 thus the upper production zone represented by the casing perforations 1b is completely isolated from the lower production zone and the gravel packing apparatus is in the same relationship with work string 300 as previously described in connection with the packing of the lower production zone the gravel carrying fluid can now be introduced through the work string 300 into the bore 262 of the cross over tool 260 of the control mandrel 200 where it will flow outwardly through the port 261 of the cross over tool 260 into the annulus 202 between the mandrel assembly 200 and the inner wall of the screen and liner.