Abstract: In the study areas,the Permian siliceous rocks consisting mainly of large amount of siliceous organic remains which dissolved into colloidal solution of SiO₂ and preserved in the sediments were formed by the replacement during the early stage of diagenesis-epigenesis.During the siliceous replacement,the original pores and path ways were filled up by replaced siliceo-us matters,the primary porosity and permeability of the rocks thus reduced.Therefore,it is unfavourable for the conversion of organisms into hydrocarbons and the subsequent migration.Nevertheless,the easily fractured siliceous rocks being frail,are favoured to forming fissured-type primary oil pools.