Editing Summary of the geology of the Grampian Highlands

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== Summary of the geology ==
 
== Summary of the geology ==
 
The Grampian Highlands are mostly made up of metamorphic and igneous rocks, part of the eroded root zone of the Caledonian mountain belt, which developed in late Precambrian to early Palaeozoic times (P915452). The name ‘Caledonides’ was given by E Suess to this mountain belt which extends from the eastern seaboard of North America to Scandinavia and Greenland; in Britian and Ireland its width is from north-west Scotland to central Wales. The Grampian Highlands portion of the Caledonides belt is very well defined by two major dislocations, the Great Glen and Highland Boundary faults [[Media:P915411.png|(P915411)]]. Late Palaeozoic and Mesozoic rocks are now found in large basins of deposition to the north and south of the Grampians and in small internal basins, but may formerly have extended over much of the region. Since Devonian times, however, the area has been mainly one of erosion. Apart from some Carboniferous rocks along the Highland Border and a small area of Permian to Jurassic rocks near Lossiemouth, the only significant post-Devonian deposits are the widespread Quaternary glacial deposits.
 
The Grampian Highlands are mostly made up of metamorphic and igneous rocks, part of the eroded root zone of the Caledonian mountain belt, which developed in late Precambrian to early Palaeozoic times (P915452). The name ‘Caledonides’ was given by E Suess to this mountain belt which extends from the eastern seaboard of North America to Scandinavia and Greenland; in Britian and Ireland its width is from north-west Scotland to central Wales. The Grampian Highlands portion of the Caledonides belt is very well defined by two major dislocations, the Great Glen and Highland Boundary faults [[Media:P915411.png|(P915411)]]. Late Palaeozoic and Mesozoic rocks are now found in large basins of deposition to the north and south of the Grampians and in small internal basins, but may formerly have extended over much of the region. Since Devonian times, however, the area has been mainly one of erosion. Apart from some Carboniferous rocks along the Highland Border and a small area of Permian to Jurassic rocks near Lossiemouth, the only significant post-Devonian deposits are the widespread Quaternary glacial deposits.
[[File:P915411.png|thumbnail|Solid geology of the Grampian Highlands. P915411.]]
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[[File:P915411.png|350px|thumbnail|P915411]]
[[File:P915452.png|thumbnail|Geological sequence and events in the Grampian Highlands.  P915452.]]
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[[File:P915452.png|350px|thumbnail|P915452]]
  
 
The only pre-Caledonian basement rocks exposed appear to be the metamorphosed acid and basic plutonic rocks of the Rhinns of Islay and Colonsay, dated as about 1800 Ma (million years old) [[Media:P915452.png|(P915452)]]; they are not correlatives of the Lewisian gneisses of the foreland to the north-west of the Great Glen Fault. The Rhinns rocks are overlain by the low-grade Colonsay Group metasedimentary rocks, whose correlation across a splay of the Great Glen Fault with the rocks on the mainland of Scotland is still uncertain, although a late Precambrian age for the Colonsay Group seems most likely.
 
The only pre-Caledonian basement rocks exposed appear to be the metamorphosed acid and basic plutonic rocks of the Rhinns of Islay and Colonsay, dated as about 1800 Ma (million years old) [[Media:P915452.png|(P915452)]]; they are not correlatives of the Lewisian gneisses of the foreland to the north-west of the Great Glen Fault. The Rhinns rocks are overlain by the low-grade Colonsay Group metasedimentary rocks, whose correlation across a splay of the Great Glen Fault with the rocks on the mainland of Scotland is still uncertain, although a late Precambrian age for the Colonsay Group seems most likely.

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