The Mesozoic is very important to the geological research in the Beijingarea, because it has a widespread distribution and a huge thickness, is a typicalvolcano-sedimentary sequence, has a tectonic setting involving the Indo-sinianand Yanshanian movements, experienced frequent magmatism, and is character-ized by rapid biotic evolution, a varity of fossil groups and abundant mineralresources. The study on the Mesozoic stratigraphy and biota is of great impor-tance both iu theory and in practice. The Triassic in the Beijing area, also known as the shuangquan Group, in-cludes three formations: Dabeisi, Tanzhesi and Xingshikou. Of the Mesozoic in the Beijing area, the Jurassic sequence is the thickest,most widespread, richest in plant fossils and most complicated in sediment types.It includes 3 series, 2 groups and 9 formations. The Cretaceous in the Beijing area is exposed in the Tuoli-Dahuichang vic-inity, covering an area of some 200 km~2. It includes 2 groups and 6 formations,yielding abundant animal and plant fossils. The area is one of the famous LateMesozoic down-faulted basins in North China.