The document discusses the geology of the Outer Hebrides region of Scotland over Earth's history. It summarizes that the Precambrian period, which makes up over 80% of geological time, would last 319 days if Earth's history was condensed to a single calendar year. Key events like the first fish, birds, flowers, and humans are noted to occur very late in the year on December 31st. The document also describes the Lewisian gneiss that forms the basement of the region and was formed in the Precambrian period over 2.5 billion years ago. It notes features like thrust faults, metasediments, amphibolites, and the effects of past glaciation that help inform the geological development

1. Professor Frank Rennie
Lews Castle College UHI
A Lewisian Perspective
The basement of the Earth

2. http://en.wikipedia.org/wiki/File:Geology_Map_UK.svg

3. Geological Time Scale
http://www.learner.org/courses/envsci/unit/text.php?unit=1&secNum=3

4. The history of Earth in a year
• Precambrian would last 319 days, until 15 Nov
• Outer Hebrides formed early Feb to mid June
• Ben Nevis & Fish appear at the end of November
• Birds appear around 19 December
• Flowers appear around 21 December
• (Skye Cuillins, St Kilda etc) around 27 December
• First Homonids around 22.00 on 31 December
• Recognisable humans on 31 Dec 23.59:49
• Last UK Ice Age 31 Dec. 23.59 +59.5 secs

5. The Geological clock
Precambrian
The rest of Earth time
First fish
First birds
First flowers
First humans

6. New Continents
Torsvik, T. H., (1998). Palaeozoic palaeogeography: A North Atlantic viewpoint. GFF 120 (2) pp109-118.

7. Smith, D. I. And Fettes, D. J. (1979).
The geological framework of the Outer
Hebrides. Proc. Roy. Soc. Edinb. 77B,
pp 75-83
The Precambrian Shield

9. http://en.wikipedia.org/wiki/File:Hebridean_Terrane.png
Lewisian outcrops

10. Banded gneiss – “grey gneiss”

11. Foliation of gneiss under a microscope

12. Amphibolite bands

14. Amphibolite pods

15. Amphibolite under crossed-polars

16. Ness metasedimentary assemblage

17. Flaggy and fractured Ness metasediments

18. Boudin
formation

19. Pod formation in a tensional environment

20. Scourie dyke

21. Pegmatitite

22. Precambrian granites cutting through Lewisian Gneiss
Dail Beag:

23. Thrust
formation

24. Metasedimentary
bedrock: Eoropie

25. Sole
Thrust:
Assynt

26. Outer
Hebrides
Thrust
line

27. Outer Hebrides
Thrust
South Harris

28. The ultramylonite – John Wilson Dougal

29. Geological Time Scale
http://www.learner.org/courses/envsci/unit/text.php?unit=1&secNum=3

30. Geology of the Outer Hebrides
Smith, D. I. And Fettes, D. J. (1979).
The geological framework of the Outer
Hebrides. Proc. Roy. Soc. Edinb. 77B,
pp 75-83.

31. Source of the Permo-Triassic Beds
Steel, R. J. and Wilson, A. C. (1975).
Sedimentation and tectonism (?Permo-
Triassic) on the margin of the North
Minch Basin, Lewis. J. Geol. Soc.
Lond. 131, pp 183-202

32. The Stornoway
Formation
Storetvedt, K. M. and Steel, R. J. (1977).
Palaeomagnetic evidence for the age of the
Stornoway Formation. Scott. J. Geol. 13 pp 263-9.

33. Line of
fault

34. The Stornoway Formation

35. The opening of the Atlantic
http://en.wikipedia.org/wiki/File:Mid-ocean_ridge_topography.gif

36. The edge of the ice-cap:
West Greenland

37. Ice
movements
Sissons, J. B. (1976). The geomorphology of the British Isles: Scotland.
London: Methuen. p 75

38. Stuc: Roche moutonee: Arnol

39. Outer
Hebridean
ice
movements

40. Glen Bhaltos:
a glacial meltwater
channel

41. Isostatic
rebound
Sissons, J. B. (1976). The geomorphology of the British Isles: Scotland.
London: Methuen p 130.

42. Brebhig: the end of moving ice

43. Raised Beach terrain at South Galson

44. North Lewis: a view south over
the ice-field

45. North Lewis glaciation
Von Weymarn, J. A. (1979).
A new concept of glaciation in
Lewis and Harris, Outer
Hebrides. Proc. Roy. Soc.
Edinb. 77B pp 97-105

46. Raised beach over glacial till, at Habost

47. Raised Beach over Till

48. Habost:
raised
beach

49. Tobha Gabhsann
:Interbedded Till
and Peat

50. Source: Quaternary geology of the Outer Hebrides. BGS Report Vol. 16 No. 2 p5

51. Quaternary Cliffs at Port of Ness

52. Habost – Eoropie: a wave-cut platform

53. West coast
morphology
Whittow, J. B. (1977). Geology and scenery in Scotland. London: Pelican. p 284.

54. Eoropie sands: a coastal dune formation

55. View this presentation again at
www.slideshare.net/frankrennie
More info at
www.lews.uhi.ac.uk/frennie
E-mail: frank.rennie@uhi.ac.uk