The genesis is discussed of a range of pedological differentiations which occur unusually deep in the soil and characterize low, but not the lowest, catenary segments of the Gundaroo pedomorpholith. This soil layer forms a large part of the soil mantle on the Southern Tablelands and is of considerable age. The deep-seated differentiations have developed as separate 'accessory' features below red-yellow and meadow podzolic, prairie soil, and red-earth sola of normal depth (2-4 ft). The zone in which they occur is termed the 'subsolum'. The features are dominated by vertical patterns related to planar and tubular voids. They include, besides a range of sesquioxidic forms, conspicuous clay differentiations comprising pronounced cutans and up to 1-1 1/2 in. wide vertical clay veins and well-developed pedality with thick colloid coatings. These features are believed to represent 'descendant' pseudogley and to be related to an unusually dynamic palaeoclimatic regime.