Zygospirae modestae plures (Brachiopoda) ad trepostoma quoddam (Bryozoa) adhaerentes, e serie Ordovicia superioriIndianae meridiorientalis
Divisio secunda ab infima constituit tam aeraePalaeozoicae quam aeonisPhanerozoicae. Abhinc 4854 ± 19 centies milium annorum coepit, antecessore Cambrio. Finem habuit abhinc 4434 ± 15 centies milium annorum, successore Silurio, secundum scalam aevorum geologicorumCommissionis Internationalis Stratigraphicae.[2] Ordovicium inceptum
ex antiquissimis fossilibus Iapetognathi fluctivagi datur.[3]
In tres series dividitur, quae inferius, medium, superius appellantur. In septem stadia dividitur, quae ab infimo ad supremum Tremadocium, Floium, Dapingium, Darriwilium, Sandbium, Katium, Himantium appellantur.[4]
Ad initium systematis Ordovicii recognoscitur exstinctionem multorum specierum circa annorum 488 milies milium incidentem. Medio systemati Ordovicio testimonia reperiuntur abhinc circa annorum 467.5 ± 0.28 milies milium magnae pluviaemeteoritarumL chondritarim,[5] deinde glaciationis,[6] deinde diversificationis specierum.[7]
Systema Ordovicium e nomine Ordovicum populi antiqui Cambriae septentrionalis appellatur. Nomen Anglicum Ordovician system a Carolo Lapworth anno 1879 definitum est e stratis eiusdem regionis quae eruditi priores aut sub Cambrio aut sub Silurio ordinabant.[8][9]
"North Wales itself — at all events the whole of the great Bala district where Sedgwick first worked out the physical succession among the rocks of the intermediate or so-called Upper Cambrian or Lower Silurian system; and in all probability much of the Shelve and the Caradoc area, whence Murchison first published its distinctive fossils — lay within the territory of the Ordovices ... Here, then, have we the hint for the appropriate title for the central system of the Lower Palaeozoics. It should be called the Ordovician System, after this old British tribe" (pp. 13-14): Charles Lapworth, "On the Tripartite Classification of the Lower Palaeozoic Rocks" in Geological Magazine decas 2 vol. 6 (1879) pp. 1-15
De historia nominis definitionisque vide: Mary Grace Wilmarth, The Geologic Time Classification of the United States Geological Survey Compared With Other Classifications, accompanied by the original definitions of era, period and epoch terms (United States Geological Survey Bulletin no. 769. Vasingtoniae: U.S. Government Printing Office, 1925) (p. 83 apud Google Books)
B. D. Webby, F. Paris, M. L. Droser, I. G. Percival (edd.), The Great Ordovician Biodiversification Event. Novi Eboraci: Columbia University Press, 2004) pp. 41 - 47
