Metamorphic in the context of Bar (unit)

The Outer Hebrides (/ˈhɛbrɪdiːz/ HEB-rid-eez) or Western Isles (Scottish Gaelic: na h-Eileanan Siar [nə ˈhelanən ˈʃiəɾ] , na h-Eileanan an Iar [nə ˈhelanən əɲ ˈiəɾ] or na h-Innse Gall, 'Islands of the Strangers'), sometimes known as the Long Isle or Long Island (Scottish Gaelic: an t-Eilean Fada), is an island chain off the west coast of mainland Scotland. It is the longest archipelago in the British Isles. The islands form part of the archipelago of the Hebrides, separated from the Scottish mainland and from the Inner Hebrides by the waters of the Minch, the Little Minch, and the Sea of the Hebrides. The Outer Hebrides are considered to be the traditional heartland of the Gaelic language. The islands form one of the 32 council areas of Scotland, which since 1998 has used only the Gaelic form of its name, including in English language contexts. The council area is called Na h-Eileanan an Iar ('the Western Isles') and its council is Comhairle nan Eilean Siar ('Council of the Western Isles').

Most of the islands have a bedrock formed from ancient metamorphic rocks, and the climate is mild and oceanic. The 19 inhabited islands had an estimated population of 26,020 in 2024, and there are more than 50 substantial uninhabited islands. The distance from Barra Head to the Butt of Lewis is roughly 210 kilometres (130 mi).

The Acadian orogeny is a long-lasting mountain building event which began in the Middle Devonian, reaching a climax in the Late Devonian. It was active for approximately 50 million years, beginning roughly around 375 million years ago (Ma), with deformational, plutonic, and metamorphic events extending into the early Mississippian. The Acadian orogeny is the third of the four orogenies that formed the Appalachian Mountains and subsequent basin. The preceding orogenies consisted of the Grenville and Taconic orogenies, which followed a rift/drift stage in the Neoproterozoic. The Acadian orogeny involved the collision of a series of Avalonian continental fragments with the Laurasian continent. Geographically, the Acadian orogeny extended from the Canadian Maritime provinces migrating in a southwesterly direction toward Alabama. However, the northern Appalachian region, from New England northeastward into Gaspé region of Canada, was the most greatly affected region by the collision.

It was roughly contemporaneous with the Bretonic phase of the Variscan orogeny of Laurussia, with metamorphic events in southwestern Texas and northern Mexico, and with the Antler orogeny of the Great Basin.