390 Proceedings of the Royal Physical Society. 



Dr Traquair further shows that the Old Eed Sandstone of 

 the Moray Firth basin can be separated into three life-zones, 

 characterised by separate groups of Fishes, viz.: — 



(«) A lower or "Achanarras" group, characterised by 

 species of Pterichthys. This is the only group 

 found on the south side of the Moray Firth. 



(6) A middle or "Thurso" group, characterised by 

 Thursius pholidotus and Coccosteus minor. 



(c) An upper or "John o' Groats " group, characterised 

 by Tristichopterus alatus and Microhrachius DicJci. 



The two latter groups have, as yet, been observed only in 

 Caithness, Sutherland, and Orkney. 



From the fact that the Fishes of the "John o' Groats" 

 group have strong affinities with fishes from the Upper 

 Devonian rocks of Canada, Dr Traquair considered that the 

 strata north of the Grampians, containing these three faunas, 

 sbould be looked on as a middle division of the Old Eed 

 Sandstone, intermediate between the Lower Old Eed Sand- 

 stone of Forfarshire and the Upper Old Eed Sandstone. 

 This view would thus revive the Middle Old Eed Sandstone 

 of Murchison. 



Dr Flett, during late years, has proved the presence of 

 these three distinct Fish Faunas in the Old Eed Sandstone 

 rocks of Orkney.^ In 1896 he recorded the discovery of the 

 "John o' Groats" beds with Microhrachius and Tristichopterus 

 in Deerness, on the mainland of Orkney. In 1898 he had 

 mapped the " John o' Groats " zone over a considerable area 

 in Orkney, and announced the discovery of Coccosteus minor 

 and Thursius pholidotus in rocks underlying the beds of that 

 zone. He also recorded a new species of Aster olepis from 

 these latter beds, which he believes to be the type species 

 of a special subzone. The Stromness beds, as has been long 

 known, hold the Fishes of the Achanarras zone of Dr Traquair. 

 Dr Flett has therefore shown that the Orkney rocks are in 

 complete accord with those of the mainland of Scotland. 



With regard to the Upper Old Eed Sandstone in Scotland, 

 Dr Tra,quair has shown that it is capable of being sub- 



1 Trans. Boy. Soc. Edin., vol. xxxix. p. 383, 1898. 



