A conveyor, comprising: a plurality of elongated, laterally spaced apart lifting/holding slats; a plurality of elongated, laterally spaced apart conveying slats, positioned between the lifting/holding slats; bearings supporting the conveying slats for longitudinal movement from a start position to an advanced position and from the advanced position back to the start position; said lifting/holding slats having upper and lower portions, said upper portion being movable vertically relative to the lower portion, between an "up" position in which upper surfaces of the upper portions are above upper surfaces on the conveying slats, and "down" positions in which the upper surfaces on the upper portions of the lifting/holding slats are below the upper surfaces on the conveying slats; first cams on the lower portions of the lifting/holding slats and second cams on the upper portions of the lifting/holding slats, wherein said lower portions of the lifting/holding slats are movable longitudinally and longitudinal movement in one direction moves the first cams against the second cams, for moving the upper portions of the lifting/holding slats from their "down" positions into their "up" positions, and longitudinal movement of the lower portions in the opposite direction causes the first and second cams to move the upper portions of the lifting/holding slats from their "up" positions down into their "down" positions characterized in that said conveyor further comprises: interlock members (93, 95, 97) for holding the first cams against the second cams as the first cams move against the second cams, wherein the interlock members (93, 95, 97) comprise lock flanges (93, 95) on said second cam and a slot in said first cam for receiving said lock flanges, said lock flanges (93, 95) and said slot extending lengthwise of the first and second cams (92, 94), said lock flanges (93, 95) having sloping lower side surfaces which function to cam the lock flanges (93, 95) into the slot with laterally outwardly extending lock surfaces of said lock flanges (93, 95) being disposed below edge portions bordering the slot. a plurality of elongated, laterally spaced apart lifting/holding slats; a plurality of elongated, laterally spaced apart conveying slats, positioned between the lifting/holding slats; bearings supporting the conveying slats for longitudinal movement from a start position to an advanced position and from the advanced position back to the start position; said lifting/holding slats having upper and lower portions, said upper portion being movable vertically relative to the lower portion, between an "up" position in which upper surfaces of the upper portions are above upper surfaces on the conveying slats, and "down" positions in which the upper surfaces on the upper portions of the lifting/holding slats are below the upper surfaces on the conveying slats; first cams on the lower portions of the lifting/holding slats and second cams on the upper portions of the lifting/holding slats, wherein said lower portions of the lifting/holding slats are movable longitudinally and longitudinal movement in one direction moves the first cams against the second cams, for moving the upper portions of the lifting/holding slats from their "down" positions into their "up" positions, and longitudinal movement of the lower portions in the opposite direction causes the first and second cams to move the upper portions of the lifting/holding slats from their "up" positions down into their "down" positions characterized in that said conveyor further comprises: interlock members (93, 95, 97) for holding the first cams against the second cams as the first cams move against the second cams, wherein the interlock members (93, 95, 97) comprise lock flanges (93, 95) on said second cam and a slot in said first cam for receiving said lock flanges, said lock flanges (93, 95) and said slot extending lengthwise of the first and second cams (92, 94), said lock flanges (93, 95) having sloping lower side surfaces which function to cam the lock flanges (93, 95) into the slot with laterally outwardly extending lock surfaces of said lock flanges (93, 95) being disposed below edge portions bordering the slot. interlock members (93, 95, 97) for holding the first cams against the second cams as the first cams move against the second cams, wherein the interlock members (93, 95, 97) comprise lock flanges (93, 95) on said second cam and a slot in said first cam for receiving said lock flanges, said lock flanges (93, 95) and said slot extending lengthwise of the first and second cams (92, 94), said lock flanges (93, 95) having sloping lower side surfaces which function to cam the lock flanges (93, 95) into the slot with laterally outwardly extending lock surfaces of said lock flanges (93, 95) being disposed below edge portions bordering the slot.