Abstract: In recent years there have existed divergent views about the isotopic ages of volcanic rocks of the Xinglonggou Formation and assignment of the strata. Through detailed geological mapping, the authors have ascertained that the two groups of U-Pb ages reported in recent years are both those of felsophyre dikes that penetrate the volcanic-sedimentary strata of the Xinglonggou Formation in this area and that the Xinglonggou Formation should be still assigned to the Lower Jurassic.