On the Existence of the Shuangtsüan Series and its Triassic Flora in Hsishan or the Western Hills of Peiping.1

The Shuangtsuan Series is a new name used for a subdivision of rocks comprising, in general, sandstones, shales, conglomerates and sometimes shales with a thin bad coal seam, with a total thickness of about 150–200 meters. The fine green and purple colors of the sandstone and shale in alteration, and variegated thin conglomerates, the frequent diabase intrusion in this series which cause the rocks of this series subjected to metamorphism, are the most characteristic features. Fossil plants collected from the shales near die coal seam at the middle part comprise the species: Psygmophyllum multipartitum Halle, Pecopteris (Asterotheca) orientalis (Schenk) Potonie, Peconteris lativenosa Halle, Newropteridium coreanicam Koiwai, Nephropsis cf. integerrima (Schmalhausen). Taeniospteris spatulata (McClelland), Nilssonia cf. simplex Oishi, cf. Danœopsis hughesi Feistm,? Albertia sp. nov., Lobatannularia heianensis (Kodaira) and Podozamites distans? (Presl.) According to the above mentioned flora, it is most probable that the Shuangtsiian Series is Lower Triassic in age. This series is sometimes overlain by the Mentoukou Coal Series or unconformably overlain by the Kiulungshan Series, and in several places it even becomes very thin or wanting, making the Hungmiaoling Sandstone directly overlain by the Mentoukou Coal Series or sometimes by the Kiulungshan Series.