An upper deck in a top flume before a lower deck in a bottom flume, each deck is adjustable from form about 10 to about 70 degrees, or from about 20 to about 45 degrees, and has a frame divided into a grid containing blank or screen panels that have openings to selectively permit smaller aggregate to pass through, while larger aggregates pass over the screens. The top flume has an opening for feeding the larger aggregates to the top of the deck adjacent the flume, and a bottom with an opening for feeding smaller aggregates under the deck. The bottom flume has an upstream side with an opening at the bottom to receive the smaller aggregates from the upstream adjacent flume and a downstream side having an opening adjacent the bottom of the side to discharge the larger aggregates, and the bottom has an opening it discharge the smaller aggregates.