Tremadoc Stage

the lowermost stage of the Ordovician system. It was identified in 1847 by the British geologist A. Sedgwick in Wales, Great Britain. In its type locality at the village of Tremadoc, it is represented by dark slates. The most important fossils of the stage are trilobites (Euloma and Niobe) and graptolites (Dictyonema and Anisograptidae). In the USSR the Tremadoc has been identified in the northwestern part of the Eastern European Platform, in the Southern Urals, in Kazakhstan, and on the Siberian Platform.