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Garvellachs
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Garvellachs
The Garvellachs (Scottish Gaelic: Na Garbh Eileacha) or Isles of the Sea form a small archipelago in the Inner Hebrides of Scotland. The islands include Garbh Eileach, Dùn Chonnuill and Eileach an Naoimh. Part of the Argyll and Bute council area, they lie in Firth of Lorne west of Lunga and northwest of Scarba and have been uninhabited since the 19th century.
The islands are known for their early Christian connections to Brendan the Navigator and Columba and for their bedrock containing rare formations in relation to the global Sturtian glaciation.
The waters surrounding the islands are extensively used for leisure sailing. Due to the array of separate tidal races produced by the underwater topography there are some treacherous stretches of water. These include the Grey Dog between Scarba and Lunga and the Gulf of Corryvreckan, between Scarba and Jura, in which is located the infamous Corryvreckan whirlpool, which is the third-largest whirlpool in the world.
The area is part of the Scarba, Lunga and the Garvellachs National Scenic Area, one of 40 such areas in Scotland, which are defined so as to identify areas of exceptional scenery and to ensure its protection by restricting certain forms of development. The Scottish plant collector, Clara Winsome Muirhead surveyed the plant life of the islands and published The Flora of Easdale and the Garvellachs in 1962.
Garbh Eileach is the largest island in the group and extends to 142 ha (351 acres) and reaches a maximum elevation of 110 m (361 ft) above sea level. The area of Eileach an Naoimh is 56 ha (138 acres) and the maximum height 80 m (262 ft). A' Chùli lies between the two and is 20 ha (49 acres) in extent with Dùn Chonnuill, the northernmost isle, being roughly half this size.
Na Garbh Eileacha is Gaelic for "the rough rocks" with the Anglicised version of the name giving rise to the archipelago's name of the Garvellachs. Garbh Eileach itself then means the "rough rock" or "rough rocky mound". Eileach an Naoimh is from na h-Eileacha Naomha and means either "the rocky place of the saint" or "the holy rocks". A’ Chùli is from Cùil Bhrianainn meaning "Brendan's retreat" and Dùn Chonnuill means "Conal's castle" and may be named after an Ulster chieftain of the first century CE.
The geology of the Garvellachs consists entirely of rocks of the Neoproterozoic Dalradian Supergroup apart from several basaltic dykes of Palaeogene age, associated with the nearby Mull Igneous Centre. The Dalradian rocks come from the uppermost part of the Appin Group and the lowermost part of the Argyll Group. The oldest preserved strata are exposed on the north of Garbh Eileach, a ~70 m thick sequence of carbonates, the Garbh Eileach Formation. The boundary between this and the overlying Port Askaig Tillite Formation is conformable. The Port Askaig Tillites are a sequence of sedimentary rocks that record a series of glacial, interglacial and periglacial episodes. This formation reaches it thickest development of 1,100 m in the area of Islay and the Garvellachs, thinning rapidly away from this region. The formation has been subdivided into five members, the lowest three of which are exceptionally well exposed on the Garvellachs. The sequence contains 48 diamictite beds, while 35–40 % of the formation is formed of sandstone of non-glacial origin, deposited in a deltaic to shallow marine sedimentary environment, interbedded with minor amounts of siltstones and dolomites.
There are two candidates within the Cryogenian period for the glacial interval represented by the Port Askaig Tillites, the older Sturtian glaciation (~717–660 million years ago) and the younger Marinoan glaciation (<654–632 million years ago), both of which are regarded as examples of a Snowball Earth, where ice sheets extended to very low latitudes. Dating of the Port Askaig Tillites has been attempted using a wide variety of techniques, but these have produced contradictory results, with evidence found that supports both of the options. Samples from the sandstones (those from the Garbh Eileach Formation and three lower members of the Port Askaig Tillite were all taken from the Garvellachs) have been analysed using detrital zircon geochronology and the results provide the strongest support for the sequence being Sturtian, with "youngest single grains" throughout being consistent with the likely depositional ages.
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Garvellachs
The Garvellachs (Scottish Gaelic: Na Garbh Eileacha) or Isles of the Sea form a small archipelago in the Inner Hebrides of Scotland. The islands include Garbh Eileach, Dùn Chonnuill and Eileach an Naoimh. Part of the Argyll and Bute council area, they lie in Firth of Lorne west of Lunga and northwest of Scarba and have been uninhabited since the 19th century.
The islands are known for their early Christian connections to Brendan the Navigator and Columba and for their bedrock containing rare formations in relation to the global Sturtian glaciation.
The waters surrounding the islands are extensively used for leisure sailing. Due to the array of separate tidal races produced by the underwater topography there are some treacherous stretches of water. These include the Grey Dog between Scarba and Lunga and the Gulf of Corryvreckan, between Scarba and Jura, in which is located the infamous Corryvreckan whirlpool, which is the third-largest whirlpool in the world.
The area is part of the Scarba, Lunga and the Garvellachs National Scenic Area, one of 40 such areas in Scotland, which are defined so as to identify areas of exceptional scenery and to ensure its protection by restricting certain forms of development. The Scottish plant collector, Clara Winsome Muirhead surveyed the plant life of the islands and published The Flora of Easdale and the Garvellachs in 1962.
Garbh Eileach is the largest island in the group and extends to 142 ha (351 acres) and reaches a maximum elevation of 110 m (361 ft) above sea level. The area of Eileach an Naoimh is 56 ha (138 acres) and the maximum height 80 m (262 ft). A' Chùli lies between the two and is 20 ha (49 acres) in extent with Dùn Chonnuill, the northernmost isle, being roughly half this size.
Na Garbh Eileacha is Gaelic for "the rough rocks" with the Anglicised version of the name giving rise to the archipelago's name of the Garvellachs. Garbh Eileach itself then means the "rough rock" or "rough rocky mound". Eileach an Naoimh is from na h-Eileacha Naomha and means either "the rocky place of the saint" or "the holy rocks". A’ Chùli is from Cùil Bhrianainn meaning "Brendan's retreat" and Dùn Chonnuill means "Conal's castle" and may be named after an Ulster chieftain of the first century CE.
The geology of the Garvellachs consists entirely of rocks of the Neoproterozoic Dalradian Supergroup apart from several basaltic dykes of Palaeogene age, associated with the nearby Mull Igneous Centre. The Dalradian rocks come from the uppermost part of the Appin Group and the lowermost part of the Argyll Group. The oldest preserved strata are exposed on the north of Garbh Eileach, a ~70 m thick sequence of carbonates, the Garbh Eileach Formation. The boundary between this and the overlying Port Askaig Tillite Formation is conformable. The Port Askaig Tillites are a sequence of sedimentary rocks that record a series of glacial, interglacial and periglacial episodes. This formation reaches it thickest development of 1,100 m in the area of Islay and the Garvellachs, thinning rapidly away from this region. The formation has been subdivided into five members, the lowest three of which are exceptionally well exposed on the Garvellachs. The sequence contains 48 diamictite beds, while 35–40 % of the formation is formed of sandstone of non-glacial origin, deposited in a deltaic to shallow marine sedimentary environment, interbedded with minor amounts of siltstones and dolomites.
There are two candidates within the Cryogenian period for the glacial interval represented by the Port Askaig Tillites, the older Sturtian glaciation (~717–660 million years ago) and the younger Marinoan glaciation (<654–632 million years ago), both of which are regarded as examples of a Snowball Earth, where ice sheets extended to very low latitudes. Dating of the Port Askaig Tillites has been attempted using a wide variety of techniques, but these have produced contradictory results, with evidence found that supports both of the options. Samples from the sandstones (those from the Garbh Eileach Formation and three lower members of the Port Askaig Tillite were all taken from the Garvellachs) have been analysed using detrital zircon geochronology and the results provide the strongest support for the sequence being Sturtian, with "youngest single grains" throughout being consistent with the likely depositional ages.
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