the third lowest stage of the Neocene system (period). It was identified by the Swiss geologist K. Mayer-Eymar in 1857. The deposits of the Helvetian stage in the Swiss Alps are marked by bluish, sandy marls full of marine fossils (the shells of such bivalvular mollusks as Ostrea, Pecten, and Cardium). The marls of the Helvetian stage amalgamate with the Molasse formation in the foremost downwarp of the Alps. Strata with marine fauna of the Helvetian stage in a cross section near Berne are covered with and underlain by freshwater deposits. In the USSR the Helvetian stage corresponds to the upper oil-bearing Maikop formations and Kotsakhur level of Transcaucasia.
B. M. KELLER