The Early Cambrian strata outcropped in South China have been concerned by geologists for long time. Mineralogical and geochemical studies have been carried out by using X-ray diffraction (XRD), X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). The results of mineralogical studies show that the clay rocks consist of illite, illite-smectite, smectite, kaolinite, quartz, mica, amphibole, feldspar, zircon etc. K2O contents of the clay rocks have a range of 4.05%~5.75% (with an average of 4.76%), which is significantly higher than the typical bentonites consisting mainly of smectite. Compared with the Earth’s crustal shales, the clay rocks have higher contents of lithophile elements such as Th, Y, Nb, Zr, Hf, Ga and U, together with lower concentrations of siderophile elements Ni and Co, and the clay rocks are also rich in As which is an indicator element in the materials resulted from volcanic activity.