The shallow-water benthos of cratonic areas distinguish different continents, and the closure of the Iapetus Ocean during the Ordovician and Silurian can be monitored by the faunas which crossed the ocean at different geological times. Brachiopod and trilobite distributions carry different palaeobiological evidence than, for example, contemporary conodont provinces, which probably reflected a combination of temperature differences and water depths. The Celtic 'Province' is reviewed, and it is concluded that each of the island faunas should be treated separately (since many have links with adjacent continents), rather than together as a province. In Newfoundland, faunas help to locate the site of the main Iapetus closure at the Reach Fault, although a substantial island arc in the Notre Dame Bay area accreted on to America in early Caradoc times. In the late Ordovician and early Silurian of Newfoundland fossils assist in the dating of quite local fault-controlled marginal basins, some of which include large olistostromes; undisturbed assemblages of brachiopods in life position give indications of the depth of water in some basins.