Based on the lithologic character, the sequence and the sediment features of the bedrocks which distribution in the typical selenosis (selenium poisoning) region in Naore Village in South Qinling Mountain, Ziyang County, Shaanxi Province, the bedrock in there is the lower part of Lujiaping Formation, and may correspond to the lower part of black shale of Qiongzhusi Formation-Early Cambrian in Yunnan Province and Niutitang Formation of Early Cambrian in Guizhou Province, South China. The bedrock of lower Cambrian in there is more than 40 meters thick of black carbonaceous siliceous slate and volcanic tuff, which selenium content is about 32 mg/kg on the average, it is the highest of all strata and rocks in south Qinling Mountain. The bedrock of the farming field, which soil has the selenium content of 16-36 mg/kg, just is this black carbonaceous siliceous slate and volcanic tuff of lower part of Lujiaping Formation of Lower Cambrian.