OLD RED SANDSTONE OF WESTERN EUROPE. 369 
some of the highest parts of the series, and thus affords the most continuous 
and complete section, particularly of the lower parts of the formation. The 
northern coast exhibits i long lines of cliff and. of shore-reef many admirable 
sections of the higher portions. No one section goes continuously from bottom 
to top of the whole succession of the Old Red Sandstone in this district. 
A traverse of the district from about the sources of the Isauld Burn in a 
northerly direction to Holburn Head probably crosses the most continuous and 
Jeast undulated succession of beds in the county; but unfortunately it is only 
at occasional intervals that the rocks along that line can be seen. Yet by 
comparing the order of the beds displayed on the coast-line with such artificial or 
natural exposures as are available inland, a tolerably complete section of the 
whole series may be constructed. 
The Old Red Sandstone of Caithness rests unconformably upon a portion of 
the altered Lower Silurian rocks of the northern Highlands. These masses are 
seen to rise from beneath it on the south-eastern coast at the Ousedale Burn, 
whence, striking inland, they form the range of the Scarabin Hills and the low 
mossy moors about the centre of the watershed between Sutherland and 
Caithness. Northward beyond this central moorland they rise again into more 
hilly ground as they approach the sea, while to the west they sweep onward 
into the rough mountainous country which extends to the Atlantic sea-board. 
No geologist can trace the relation of this platform of old crystalline rock to the 
unconformable and usually little disturbed strata which cover it without being 
struck by the smgular unevenness of its surface, and by the evidence that this 
tugged character existed at the time when the Old Red Sandstone was laid down. 
At the eastern end of the Scarabin Hills, the Berriedale Water has cut a deep 
transverse section across this uneven platform, and shown how its inequalities 
are wrapped round by and buried under the conglomerates of the later forma- 
tion. Yet from this marginal belt—doubtless a shingly beach at the beginning 
of the Old Red Sandstone deposits—the Scarabin range towers steeply to a 
height of 1600 feet. Knobs of the same ancient surface rise up among the 
sandstones and flagstones to the north and west, as at Dirlet Castle, Isauld 
Mill, Port Skerra, and Coalbackie, near Tongue. The platform upon which the 
Caithness flagstones and conglomerates were deposited must have been not 
unlike portions of the country lying to the westward from which these over- 
lying strata, once far more widely extended in that direction than now, have 
been removed. Another feature, even more readily recognised by the observer, 
is the constant relation between the nature of the rock constituting the plat- 
form and the character of the overlying conglomerate. Towards the southern 
_ corner of Caithness the underlying crystalline rock is chiefly a rather fine- 
grained pink granite. Further north this gives way to flaggy micaceous gneiss, 
dark greywacke, and quartz-rock, which in turn, dipping gently towards north- 
VOL. XXVIII. PART II. oD 
