The Question of Primordial and Cambrian/Taconic: Barrande and Logan/Marcou

Joachim Barrande in 1846 recognised the Primordial Silurian fauna as the oldest of three faunas he identified in stratigraphic order in Bohemia. A key point in development of the early Paleozoic stratigraphic column was Barrande's 1850 identification of elements of his Primordial fauna in Great Britain. The link between rocks comprising the Cambrian System and a distinctive fauna was a factor in the eventual acceptance of the validity of the system that Sedwick had named.

A decade later, Barrande also recognized the Primordial fauna as occurring in the Taconic System of Emmons in eastern New York and western Massachusetts. Despite arguments from the beginning as to the geologic basis of this system, some geologists used it in a more widespread sense in New England and Canada. William Logan eventually realized that structural complexities near Quebec City provided a spurious sequence of faunas in supposed correlatives of the Taconic. With interpretation of a younger age for the Quebec Group, Logan took this group out of the Taconic and effectively removed "Taconic" fossils from much of Canada, thereby helping restrict usage to the type area.

Jules Marcou vigorously defended priority of the Taconic. He repeatedly published that Barrande was essentially ignored or injured by Logan. Correspondence, both published and private, demonstrates that this is not the case; they mutually respected each other's scientific abilities. Marcou, and a small but vocal minority of American geologists, supported the use of Taconic during the 1870's and 1880's, but discovery by Walcott in 1887 of Ordovician fossils in Massachusetts Taconic rocks effectively ended debate as to priority of Cambrian.