
OLD RED SANDSTONE OF WESTERN EUROPE. 419 
Noup and Sand Ness, cut off from the red quartzite and altered sandstones 
to the south by a fault, resembles part of the Bressay series, but is redder 
in colour, and is invaded here and there by a pink or salmon-coloured 
porphyry. It is on the opposite island of Papa Stour, however, that the 
most instructive sections are to be seen. Exposed to the full sweep of 
the Atlantic storms, the coast-line of that island presents a picture of 



































































































































































































































































































































































































































































Fig. 10.—View on the West Side of Papa Stour. (Island of Foula in the distance.) 
utter ruin,—of solid rocks stubbornly standing their ground, yet trenched, 
and splintered, and crumbling under the assaults of the ocean-battery ; 
cut into caverns, and arches, and into isolated stacks and skerries, which, 
rising in advance of the present cliff, serve to mark how much it has receded. 
The fundamental rocks of the island consist of purple sandstones and flags, 
with bands of quartzose and felspathic conglomerate. These strata are seen 
on either side of the chief bay on the east side of the island. They have a 
south-westerly dip, but cannot be followed westwards in ascending section, 
owing to a large mass of pink porphyry which occupies the higher ground, and 
appears to have broken through and to overlie them, At the southern end of 
the island, however, similar flaggy sandstones, having a westerly dip at 20°, and 
therefore, it may be presumed, stratigraphically higher than those on the east 
side, appear on the shore. They are interstratified with several successive beds 
of a dull, dirty green, sometimes very amygdaloidal and slaggy diabase- 
porphyrite. These igneous rocks closely resemble some of the typical diabase- 
porphyrites of the Sidlaw, Ochil, and Pentland Hills, and may without hesitation 
be regarded as contemporaneous lava-streams in the Old Red Sandstone of this 
part of Scotland. Fragments of similar rocks abound in the conglomerates and 
sandstones below and above them, so that their truly coeval eruption is put 
