1. A classifier for the classification of granular material comprising a classifier housing ( 10 ) having a V-shape in vertical section with first and second legs and including a stairway cascade ( 13 ) in said first leg, said stairway cascade ( 13 ) lying obliquely at an angle departing from the vertical and said stairway cascade being permeable for passage for classifying gas there through, a classifying gas intake duct in said first leg directing classifying gas to said stairway cascade and classifying flues ( 15 ) lying one above the other and obliquely downwardly inclined in louver fashion in said second leg, said classifying flues ( 15 ) defining classifying ducts therebetween and being positioned to define a classifying zone ( 14 ) between said stairway cascade ( 13 ) and said classifying flues ( 15 ), a feed inlet opening ( 16 ) for a classification feed on the top of said housing ( 10 ) and above said classifying zone ( 14 ), an oversize fraction discharge openings ( 18 ) on the bottom of said housing ( 10 ) below said classifying zone ( 14 ) for the discharge of an oversize fraction of said granular material and upwardly extending guide vanes ( 21 ) at the upper end of said classifying flues ( 15 ), said guide vanes being adjustable to control the velocity of said classifying gas passing through said classifying ducts.