378 PROFESSOR GEIKIE ON THE 
The red shales and sandstones of Braemore are sometimes pitted as if by 
rain-prints, but have as yet yielded no fossils. In a sandstone at Ulbster, Mr 
C. W. Peacu and Mr SHEARER found plates of Pterygotus. As this crustacean 
genus has been supposed to be characteristic of Lower Old Red Sandstone and 
Upper Silurian strata, Sir RopErick Murcuison naturally regarded its occur- 
rence here as proof that the red sandstones of Sarclet belong to the Lower Old 
Red Sandstone, the overlying flagstones, devoid of Pterygotus, being placed in 
the middle of the system.* It ought to be noted, however, that distinct grey 
calcareous flagstones of the true Caithness type occur below the horizon from 
which the specimens were obtained at Ulbster; so that, at all events, the 
remarkable physical conditions to which the Caithness deposits were due had 
begun before the formation of the Pterygotus sandstone. Not only so, but this 
genus appears to have survived far into the time of the true Caithness flags. 
Mr Peacu found some pieces, probably of Pterygotus, in one of the calcareous 
flagstones at Kilmster, near Wick, which is well up in the lower flagstone 
group. Again, in Orkney, from a bed high in the upper flagstones, a well- 
sculptured fragment of Pterygotus has been obtained. If, then, this genus be 
assumed to mark a zoological platform not higher than the inferior parts of the 
Lower Old Red Sandstone, we must assign a considerable part of the Caithness 
flagstones to that position. 
With regard to the extension of the Braemore sandstones and shales, it 
may be remarked that though, owing to the overlap of higher strata, that group 
is concealed towards the north, except at the Sarclet anticline, red sandstones 
of similar aspect are seen below the conglomerate which far to the west caps 
the hills above Tongue. These westward prolongations of the lower parts of 
the Caithness system will be referred to in a subsequent paragraph. 
3. Badbea Breccia and Conglomerate.—By far the most conspicuous 
member of the Old Red Sandstone series in the south of Caithness is a 
remarkable breccia or brecciated conglomerate which crowns the heights 
to the east of Ousedale and above Badbea, and projects in a line of rough 
broken escarpment. For nearly a mile and a half its edge runs approxi- 
mately parallel with the coast-line, until by a rapid change of dip and 
angle it turns round, and, dipping towards the north-east, descends to 
the sea and passes under higher strata. It occurs in thick beds, wherein little 
or no trace of stratification may be found. The stones, considerably smaller 
than in the basement conglomerate of Braemore, seldom exceed five or six 
inches in length. They consist mainly of pink cleavable orthoclase, pink 
granite, grey quartz-rock, white vein-quartz, and occasional pieces of red sand- 
* “ Siluria,” 4th edit. p. 256. 

