I Chap. XI.] OLD BED IN THE NOETH OF SCOTLAND. 
259 
largely increasing demand for its valuable flagstones, the hard and sterile 
parts of Caithness may become a well-peopled and industrial tract. 
Besides fossil Fishes, the Caithness flagstones contain innumerable shells 
of Estheria (a small bivalved Crustacean) and numerous fossil Plants ; and 
these organic remains will presently be considered *. 
Continuing to trace the ascending order of the Old Eed Sandstone series 
of Caithness into the Orkney Islands, it is to be noted that the flagstones, 
usually of a dark-grey colour, but here and there of a purplish tint, gra- 
duate upwards into those higher light-red and yellow sandstones and grits 
which, constituting the northernmost point of the mainland, Dunnet Head, 
are again seen at Hoy Head and in many parts of the Orkney and Shet- 
land Islands, where they occupy a similar relative position. Some of these 
upper sandstones (e, p. 255), into which there is a perfect transition from 
the harder flagstones, might in hand-specimens often be mistaken for the 
beds which underlie the Caithness flags, both in colour and composition. 
Others are light- coloured, yellowish, fine-grained freestones, notably in 
the Isles of Pomona, Shapinsha, and Eda. In these upper sandstones 
Land Plants prevail, particularly in the Shetland Isles ; and according 
to Dr. Hooker they are referable to Calamites, generically resembling, but 
of species differing from, the forms known in the Carboniferous rocks f. 
Seeing that there, is no sign in this northern region of a further passage 
upwards into any strata which can be classed as Carboniferous, the triple 
subdivision of the Old Eed Sandstone which I have long recognized is 
adhered to. The equivalents of this great series will afterwards be noted 
in other parts of the world, and especially in Russia, where strata occupying 
the same place in the general series of deposits are found to contain the 
Mollusca of Devonshire commingled with the Ichthyolites of Scotland. 
The same succession, from lower conglomerate and sandstone to over- 
lying Fish-beds, which occurs at Dunnet Head and the Orkney Islands is 
exhibited between the interior crystalline rocks and the coast in the counties 
of Inverness, Nairn, Elgin, and Banff; but in this range the Upper Old 
Eed is wanting 
The extent to which the variation of the lithological characters of the 
deposits in their range southwards has affected the distribution of the 
organic remains is explained in the sequel. 
Animal Remains of the Old Bed Sandstone. — "When Agassiz completed 
his remarkable analysis and history of the fossil Fishes of this deposit, the 
number of species enumerated from Britain alone amounted to sixty-five ; 
and this number has since been augmented. Eeferring the student to 
* The most extensive quarries are situated a 
few miles east of Thurso, having been opened out 
upon a very large scale by Mr. Gr. Traill, M.P., 
of Castle Hill. The flagstones are occasionally of 
gigantic dimensions, and often present casts of 
Plants upon their surface. 
t See Quart. Journ. G-eol. Soc. Lond. vol. ix. 
p. 49, and further on, p. 271. 
I The late Lady G-ordon Cumming, of Altyre, 
was the discoverer of many of these fossil Fishes ; 
and the exquisite manner in which that accom- 
plished lady and her eldest daughter sketched 
and coloured them is duly recorded in the pages 
of Agassiz's classic work. (See Poissons du Vieux 
Grres Eouge, passim.) 
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