The (possible) extent of Avalonia
The Avalonian remnants include, from east to west, the northwest corner of Poland starting around Szczecin; the northern chunk of Germany; possibly a sliver of Denmark; all of the Netherlands; almost all of Belgium; the Calais/Dunkirk area of France; all of England and Wales (but almost none of Scotland); Ireland southeast of a line from Drogheda to the Shannon estuary; southeastern Newfoundland (including the Avalon peninsula which gives Avalonia its name), with St Pierre and Miquelon; Nova Scotia except the parts south of Halifax; Prince Edward Island; New Brunswick roughly south of Monckton and Fredericton; Maine southeast of the Norumbega Fault which runs southwest from the border to Bangor and then more SSW to Portland, possibly including also the coastal strip of New Hampshire; Massachusetts southeast of a line from the lower Merrimack river valley to Worcester, however excluding Cape Cod ; all of Rhode Island; and finally Connecticut east of Hartford and New Haven. (But not Long Island, just across the Sound.) It's a remarkable mythic assemblage, from Pomerania to Providemce, including both the Avalon Peninsula and the original Isle of Avalon.
The precise borders are debatable, because Avalonian sediments are found at many depths, and it consisted of a series of islands anyway; one map puts remnants in the Carpathians, and also straddling the Straits of Gibraltar. Wikipedia page offers several options, including these:
Avalonia in Europe (one version)
Avalonia in Europe (another version)
The end of Avalonia (one version)
The end of Avalonia (another version)
Avalonia, when it existed, started at the South Pole, an arc of volcanic islands on the rim of Gondwana, bordering land now in Mauretania/Gabon, South Carolina/Georgia/Alabama, and Venezuela/Colombia. When it split off about 490 million years ago, at the end of the Cambrian, it set sail into the Iapetus Ocean, opening up the Rheic Ocean behind it. About 450 million years ago, at the end of the Ordovician, Avalonia joined onto the slightly larger continent of Baltica as a peninsula, and during the Silurian period closed up the Iapetus Ocean, merging with the northern continent of Laurentia. The rest of Gondwana eventually caught up behind it, closing the Rheic Ocean and bringing most of what is now Europe together during the Devonian as the supercontinent of Pangaea formed.
There's a lovely iPad app which lets you assemble Pangaea at your leisure (and another which lets you dismantle it). These screenshots show the history of Avalonia, the red pin marking my Belgian home.
Anyway, greetings, fellow-citizens of the former Avalonia! I bet you never realised that we had that in common.