The SB1 drilling was carried out in the central part of Lake Shinji by the Geological Survey of Japan in the 1960's，and a precise pollen analysis study was carried out by late Professor Onishi. He established seven pollen zones (and 14 subzones) mainly on the basis of this work，and these are widely applicable to the San'in Region. We have recently discovered the Akahoya Tephra(erupted 6,300yrs B.P.)from one of his preserved samples，the horizon of which can be correlated with the lower part of the Cyclobalanopsis-Castanopsis pollen zone(Onishi，1990). Other drillcores from in and around Lake Shinji have also been reexamined. The environmental changes of the Lake Shinji area are discussed in the light of these new findings.13;