While examining the petrographic material I collected in 1914 during geological studies in the Middle Vitim Mountain Country, I encountered among the limestone specimens examples in which a well-preserved oolitic deposit could be observed under the microscope, only partially masked by subsequent recrystallization. The considerable interest presented by the discovery of oolitic formations among the metamorphic rocks of the Vitim Plateau prompted me to familiarize myself in more detail with oolitic structures using material where the primary structure was not be obscured by secondary alterations.