400 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DoC. 1, 



mica-schist and gneiss are tlie smallest and least abundant materials. 

 The largest boulders in this coarse conglomerate are about four feet 

 in length, and, differing from those of the breccia of the east of 

 Sutherland, they are all rounded. The dip of all these beds is also 

 70° to the W.N.W., or sharply inland, thus seeming to throw the 

 Old B,ed Sandstone of the Black Isle iuto a trough. 



Succeeding to these coarser conglomerates, but alternating with 

 pebble-beds, are the chief freestones of the group, which are so 

 extensively used for building-purposes throughout the counties of 

 Ross, Cromarty, Inverness, !Nairn, Moray, &c. This sandstone, of 

 which quarries are opened in nimiberless localities, is of very varied 

 tints of red, is occasionally much variegated either by greenish and 

 whitish spots of earthier matter (Thon-Gallen of the Germans), or by 

 a regularly ribboned or striped structure of thin layers of deep red 

 alternating into lighter and yellowish laminae of deposit. In short, 

 we find iu the rock those lithological features, which in the early 

 days of geology were erroneously supposed to be characteristic of 

 the New Red Sandstone only, but which are now known to be 

 prevalent not only in the Old Red, but also in the red and variegated 

 Lower Silurian or Caradoc freestones of Shropshire. In the lower 

 conglomerate and sandstone, as well as in the overlying gritty and 

 pebbly beds with fine building-stones, organic remaias have as yet 

 been very sparingly found — a scale or two of a fossil fish being all 

 that I have heard of; and whether it be on the coast of Cromarty, 

 or at Strathpeffer in the interior of Ross-shire, it is only when we 

 reach certain schistose beds, often more or less bituminous (the 

 equivalents of the Caithness Elags), that fossil fishes begin to be 

 distinctly recognized. 



No identifiable organic remains have as yet been detected in the 

 lower sandstones and conglomerates of this series in the North of 

 Scotland ; yet these thick and finely levigated masses are considered 

 by me to represent in time the lowest beds of the Old Red of Eor- 

 farshire, Shropshire, and Herefordshire, which contain Pterygotus, 

 CepJialaspis and Parka decipiens — ^remains which are quite distinct 

 from those of the bituminous schists and flagstones of Caithness. 



Caithness Flags, or Middle Division of the Old Red Sandstone of 

 the N.E. of Scotland and the Orkney Islands {d of the section, fig. 9, 

 p. 394). — Having indicated in the General Section, fig. 9, and in 

 figs. 10 and 11, that the Lower Old Red Sandstone and Conglomerate 

 pass up gradually into the Caithness Plags, it is manifest that the 

 latter can no longer be ranked, as they have been, vn.th the lower 

 member of the group, — the more so as I have shown that the 

 ichthyolites they contain are in other parts of the world associated 

 with shells which characterize the middle and upper divisions of the 

 Devonian rocks*. In no part of the British Isles are these fiagstones 

 so copiously elaborated, and so rich in fossil fishes, as in Caithness 

 and the Orkney Islands. It is unnecessary that I should here pre- 

 sent to the reader accounts of the numerous variations in litholo- 



* Russia in Europe, vol. i. p. 64 ; Siluria, new edit. p. 382 ; and infra, p. 414. 



