Introduction to the boundary between Archaean and Proterozoic: The geological age of the Changzhougou Formation of the Changcheng System at the bottom of the middle and Upper Proterozoic section in Jixian is about 1.8 billion years, while the age of the lower Archean metamorphic rocks is about 2.5 billion years, with There is obvious angular unconformity and ancient weathering crust. In between, about 700 million years of geological record are missing.