Abstract
The procedure of first defining a time boundary between the Silurian and Devonian Systems and postponing the designation of a stratotype leaves stratigraphers without guidance as to which series the Silurian should be divided into and which corresponding epochs would be practicable for reference in international work. The situation in Europe is reviewed with respect to established usage, and it is found that with present concepts Silurian series based on the succession in the Welsh Borderland and in the Barrandian can be made compatible in the critical part of the succession. A natural consequence of the establishment of a system boundary at the base of the zone with Monograptus uniformis would be the redefinition of the Downtonian as proposed by Allen & Tarlo 1963, to be used subsynonymously with the Pridolian.
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