266 
SILUKIA. 
[Chap. XI. 
forms, Holoptychius Flemingii and Platygnathus Jamesoni, Ag., are com- 
mon to the uppermost zone of this group in Scotland and Eussia. 
I entertain no doubt that these yellow sandstones (with red layers) of 
Dura Den pertain truly to the Old Red group — that they are entirely sub- 
jacent to the adjoining yellow Carboniferous sandstones with Coal Plants. 
A splendid specimen (now at Rossie Priory) of Holoptychius Andersoni, 
three feet long, was found on the occasion of a visit I made to Dura Den 
in company with Lord and Lady Kinnaird and the late Rev. Dr. J. Ander- 
son ; and, as a form very similar abounds also in the lower red portions 
of the deposit (at Clashbinnie), the age of the yellow sandstone of Fife is 
clearly substantiated. 
Some Fishes and certain Plants, of which we shall presently speak, 
range up from the Caithness beds into the sandstones of the northern 
headland of Dunnet and the Orkney Islands. 
Whilst I adhere to that triple classification of the Old Red Sandstone of 
the North of Scotland which I correlated with the similar arrangement of 
the Devonian rocks of Devonshire and the Rhine *, particularly where the 
series extends from the Ord of Caithness northwards into the Orkney and 
Shetland Islands, I have to announce that in respect to the age of the 
uppermost light-coloured sandstones of Burgh Head and Lossie Mouth, 
south of Elgin and of Tarbet Ness (Ross-shire), I have now abandoned 
the suggestion of classing them with the Old Red or Devonian rocks. 
Stratigraphically considered, the strongest grounds indeed still exist to 
induce the field-geologist to connect these reptiliferous sandstones with 
the subjacent Old Red Sandstone, on which they repose conformably, as 
shown in my last edition. In the environs of Elgin I have three times 
examined these rocks, and on the last two occasions in company with my 
accomplished friend the Rev. G. Gordon of Birnie, and once when aided 
by Professor Ramsay. In advancing from the crystalline rocks on the 
south, and passing through the lower zones of Old Red Sandstone with 
numerous characteristic Ichthyolites, and from them through the chief 
yellow sandstones north of Elgin with their peculiar fossil Pishes, into the 
sandstones of the coast, I could detect no unconformity between all these 
beds with Ichthyolites and the strata of rather lighter colour, and contain- 
ing concretionary cornstones, also like Old Red Cornstones, which extend 
to Burgh Head and Lossie Mouth. It is in these last-mentioned rocks 
that the remarkable Reptiles the Telerpeton (Mantell), the Stagonolepisf 
(Agassiz), and the Hyperodapedon (Huxley) have been found. 
Again, numerous footprints of Reptiles were found on the surfaces of 
these sandstones, whether between Burgh Head and Lossie Mouth in 
Elginshire or near Tarbet Ness in Ross -shire. In the last-mentioned 
district various geologists have confirmed the original observations of Pro- 
fessor Sedgwick and myself (1827), showing that all these strata seem to 
* See last edition of' Siluria,' Table, p. 433. 
t Shown to be a Crocodilian Reptile by Huxley. 
