In the research of stratigraphy, first is to establish the lithostratigraphic units, then it is possible to research the palae-ontological character and the time limit of rock units in different sides and the extending range in detail. 在地层学研究中,首先建立岩石地层单位序列,然后才有可能详细地研究各个岩石单位在不同地点以及在整个延展范围内的古生物学特征和时限。