420 MR JOHN S. FLETT ON 



place, and vast periods of time to elapse. Before the deposit of the upper Old Red of 

 Hoy, much of the Orcadian Old Red had been stripped from the surface of the Orkneys, 

 and very considerable dislocations had modified entirely the old physiography and 

 structure of the country. 



III. — Comparison with the Old Red of other Districts. 



Such being in its main features the structure of the Orkneys, and the subdivisions 

 which can be established by the distribution of the fossils, it remains to be considered 

 how far these conclusions can be applied to other districts in which rocks of like age and 

 similar fossils occur. 



The John o' Groats Beds and the Eday Sandstones. 



As regards the uppermost beds, the inquiry is a simple one. Rocks containing 

 the same fossils occur in only one locality — the north-eastern angle of Caithness; 

 and here their lithological characters so strikingly resemble those of the Orkney 

 beds that no difficulty whatever can be felt in accepting their zonal identity. The 

 John o' Groats beds of Caithness are, then, to be correlated with the Eday, Deerness, 

 and South Ronaldshay sandstones of Orkney. Sir A. Geikie gives a list of the fossils 

 which have been found in this series in Caithness.* He enumerates, in addition to the 

 three type fossils, Acanthodes Peachi (Eg.) and Glyptolepis leptopterus (Ag.), neither 

 of which is known to be present in the similar beds of Orkney. It is remarkable how in 

 both counties the fishes characteristic of the lower rocks have been superseded by new 

 types so completely that almost no trace of their persistence is to be obtained. The 

 uppermost zone of the Orcadian Old Red is thus a well characterised one, and may be 

 designated, from the locality in which alone it was known to occur for many years, 

 The John o' Groats Sandstones (zone of Tristichopterus alatus, Egert.). 



The Thurso and Rousay Beds. 



For the representatives elsewhere in Scotland of the lower zones, we must look to 

 two localities, to Cromarty, from which Hugh Miller and Agassiz early in the century 

 furnished a list of fossils, and to Caithness, where, since the time of Hugh Miller and 

 Robert Dick, much work has been done in the palaeontology of the Old Red. The earlier 

 work has subsequently been subjected to thorough revision, and a wealth of new 

 material been brought to light by Dr Traquair, to whose papers I am greatly indebted, 

 and on whose published statements I shall rely in comparing the lists of fossils from 

 each locality. In his paper, " Achanarras Revisited " (1894), t he has briefly stated the 



* Sir A. Geikie, Old Red Sandstone, p. 404. 



t Traquair, Proc. Roy. Phys. Soc. Edin., vol. xii., 1894. 



