318 DR JOHN S. FLETT 



however, hardly strengthens the comparison. The Shetland beds are coarser, more 

 micaceous, and less uniform than those of Orkney. Clearly they were formed by the 

 denudation of a slaty and gneissose series, like that which forms the axial ridge of 

 Shetland. Evidence of this sort does not carry much weight ; but we may note that 

 the Old Red Sandstone of Shetland certainly resembles the Caithness beds in litho- 

 logical character more closely than the Upper Old Red Sandstone of Hoy, Ross-shire, 

 and the districts south of the Moray Firth. 



Summary. 



In speculating on the age of the Shetland beds, the character of the vertebrate fauna 

 is by far the most reliable index ; and next to it we may place the evidence of the 

 plants. The former points unmistakably to Upper Old Red conditions, the latter to 

 close affinities with the Orcadian. The conclusions which at the present time we are 

 justified in arriving at may be summarised as follows : — 



(1) The Old Red Sandstone beds of Shetland belong to a distinct zone of that 

 system, different from any other yet identified in Britain. 



(2) By the evidence of its fossil fishes, it is most naturally placed in the Upper 

 division. 



(3) Both the fauna and the flora indicate affinities with the Orcadian or Middle Old 



Red of Caithness and Orkney, consequently it may be the lowest or one of the lowest 

 zones of the Upper Old Red Sandstone. 



(3) 



LITERATURE. 



(1) Bouk, Ami, Essai Geologique sur I'Ecosse, p. 114 (n.d. probably 1820). 



(2) Fleming, J., Mem. Wernerian Soc, vol. i., p. 174 (1808). 

 Flett, John S., " On the Discovery in Orkney of the John o' Groat's Horizon of the Old Red Sandstone," 



Proc. Roy. Phys. Soc. Edin., vol. xiii., p. 255 (1896). 

 „ „ " The Old Red Sandstone of the Orkneys," Trans. Roy. Soc. Edin., vol. xxxix., p. 383 



(1898). 

 Ibid., p. 409 (1898). 



Memoir of Sir R. Murchison, vol. i., p. 139 (1875). 

 "The Old Red Sandstone of Western Europe (Part I.)," Trans. Roy. Soc. Edin., 



vol. xxviii., p. 345 (1878). 

 "The Old Man of Hoy," Geol. Mag., p. 49 (1878). 

 Geological Sketches, p. 76 (1882). 

 Text-Book of Geology, p. 1010 (1903). 



Geological Map of Scotland (published by Bartholomew, Edinburgh). 

 Tram. Roy. Soc. Edin., vol. xxviii., p. 418 (1878). 

 Text- Book of Geology, p. 1012 (1903). 

 Gibson, George, Hie Old. Red Sandstone of Shetland (1877). 



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