在北京西南郊的长辛店附近出露着长辛店组砾岩。根据砾岩中产出的鱼鳖类未定种化石残体以及砾岩的岩性与产状等特征,周明镇先生断定:“砾石层的时代应为第三纪初,最新不能晚于渐新世后期”。1977年,翟人杰同志根据最新发掘出的四个种的哺乳动物化石,讨论了长辛店组沉积的时代。他认为该层属于早第三纪晚始新世。可见,长辛店组砾岩是北京平原边缘出露的最古的新生代地层。 Nearby Changxindian in the southwestern suburbs of Beijing is the Changxingdian conglomerate. According to the characteristics of undetermined fossil remains and the lithology and occurrence of conglomerates produced in conglomerates, Mr. Zhou Mingzhen concluded: “The age of the gravel layer should be early Tertiary, and the latest can not be later than gradual Later period. ” In 1977, Comrade Zhai Jiejie discussed the age of the Changxindian Formation deposition, based on the newly discovered four species of mammalian fossils. He believes that this layer belongs to the Late Eocene late Eocene. Visible, Changxindian conglomerate is the edge of the Beijing Plain exposed the most ancient Cenozoic strata.