Die Liegendgrenze des Karbons im Lichte biostratigraphischer Kritik
Compte Rend Congres Avanc Etudes Strat Carbonifere Heerlen 1927: 651-661
Since the racial development of different groups of organisms is not synchronized, the boundary between geologic systems should be drawn at various horizons depending on which groups of fossils are taken as a criterion. The author proposes to give the decisive role in each case to that class of animals which was at the time most vigorous, and preferably one which can be used for minute zoning. Accordingly the cephalopods are relied upon to establish the Devono-Carboniferous boundary, which falls at the top of the Gattendorfia beds.