Description of the areaThe area investigated is located in the southwestern part of Kiangsu Province, between Longitude 118°30’ and 119°8’ E. and Latitude 31° 40’ and 32°15’ N. The whole area is about 1740 square kilometers.The topography is moderately rugged. The ranges of hills are distributed at the northeast and southwest parts of the area, with elevations varying between 200-400 meters. The remainder of the area is occupied by the flat recent alluvial plain of the Chinhwaiho. This river has its course commencing from the southwestern hills and flows into the Yangtze River.