Middle and Upper Devonian (Voronezh, Belgorod regions of Russia) and Early and Middle Carboniferous (southern flank of Moscow sedimentary basin) paleosols were studied in detail. It was shown that the specificity of clay mineralogy of studied paleosols (with few exceptions) is their monomineral composition. Devonian terrestrial deposits and paleosols developed from them are kaolinitic, rare they have berthierine composition. Early Carboniferous paleosols are smectitic and Middle Carboniferous — palygorskitic. The mineralogy clear reflects the trends towards the aridization of climate and shifts in climatic zonation. Monomineral compositions and the absence of interstratification are the principal differences between Paleozoic, and Quaternary paleosols and modern soils developed from terrigenous deposits. The main reason behind it is the juvenile nature of Paleozoic paleosols from one side and the re-cycling of material from which Quaternary soils are developed – from other