The examination of the last appearances of animal genera and species through the Early Palaeozoic showed that there was a mass extinction at the end of the Ordovician in China. This event occurred before the zone of Glyptograptus persculptus **) and affected a wide range of unrelated groups, both benthic and pelagic (Mu et al. ]974, 1984 I Rong 1979, 1983, 1984 I Mu 1983; Chen& Lenz 1984). This conclusion is drawn on account of material which has been obtained during the last two decades. A great number of sections across the Ordovician-Silurian boundary have been studied in China. Continuous sequences, representing Ashgillian and an Early Llandoverian interval, are still relatively common in this country (Mu 1983), although the effects of eustatic sea-level fall and regional or local uplift during the Ashgillian caused unconformities between Ordovician and post-Ordovician rocks in North China and other areas, where at least Silurian has not been deposited. The sequences across the O-S boundary in northwest China, northernmost China, and southern South China are mostly continous, with great thickness, but complicated in geologic structure, and rare in fossils (Mu 1983). That is not the case for the central-southwestern China (Yangtze) and Tibet-western Yunnan regions, especially in western Hubei and the border area of Sichuan and Guizhou Provinces, where the Ashgillian and early Llandoverian rocks are unusually well represented by platform deposits, far less in thickness, rich in fossils (both benthic and pelagic) with good exposures. Therefore, all data discussed herein, came from these regions. The Wufeng Formation (Ashgillian) and the Lungmachi Formation (Llandoverian) are composed mainly of siliceous shales and contain abundant graptolites. Between these two formations, there is a thin bed, the socalled Kuanyinchiao Bed, consisting mainly of mudstone, argillaceous limestone and silty shale, in which a shelly fauna, i.e. HirnantiaDalmanitina Fauna, is present. The graptolite successions associated with this shelly fauna are as follows: