The authors selected zircon, tourmaline, quartz and feldspar from 67 samples of different facies on the coast of Guangdong for ultrastructural observation with a magnification from 300 to 10, 000 under an electron scanning microscope. It has been found that the mineral grains vary ultra-morphologically from place to place, suggesting the influence of different environmental factors. The grains from rivers mostly show simple but irregular collision pits, some being disc-shaped or desqua- mated, which probably resulted from physical erosion. The exposed areas have yielded rounded grains covered with mini-pores, fissures and funnel-shaped corrosion pits, suggesting a physical erosion together occasionally with chemical corrosion. The morphology of the rounded grains from some periodically exposed facies zones, e. g. intertidal zone, is varied, assuming shell-or honeycomb-shaped raini-pits, small directional striae, curved fissures, V-shaped corroded pits and some Si02 precipitates, which are considered to have been formed by physical erosion in combination with chemical corrosion. An equally complicated texture was also found at the surface of the mineral grains from the underwater zones. It is characterized by honeycomb, corroded pits, irregular or parallel fissures, curved stepIike and funnel-shaped corroded pits as well as Si02 precipitates. This texture is probably a product of chemical corrosion associated with a joint physicalchem ical corrosion. All these characters seem to indicate the origins of different facies zones in this particular coastsl area.