The Yishui area is located in the middle part of the Tancheng----Lujiang fault belt,where volcanic rocks erupted intensively in the Mesozoic.There are two phases volcanic activities.The first phase volcanic rocks are intermediate volcanic rocks of high potash calc-alkalic series.Their ages are110--125 Ma.According to K60 calculation in andersite ,the thickness of crust is 58--62km,demonstrating that there is orogenic root in this period.It formed in an active continental margin environment.The second phasevolcanic activity belongs to intermediate--acid volcanic rokds of shoshonite series.Their ages are 69--101Ma.Eu anomaly of the volcanic rocks is not apparent.δEu=0.92(average).It formed in a lithospheric thinning and extension environment with orogenic root.The later Cretaceous river and lake faces sedimentary rocks,namely Dasheng Group,3200m thick,is formed in the environment of orogenic collapse, extension of crust if the fault basin in Tancheng--Lujiang fault belt.