416 PROFESSOR GEIKIE ON THE 
From Gulber Wick to Lerwick a series of promontories and inlets with rocky 
sides reveals the characteristic features of the Old Red Sandstone of Shetland. 
But if we take the exposures at the north end of Bressay Sound and connect 
them with those from the north-western extremity of Bressay to the precipice 
of the Noss Head, we obtain a nearly continuous section across the strike of — 
the strata, and see the thickest succession of beds in this region. A dislocation | 
of the strata occurs near the north-west end of Bressay, by which perhaps some 
of the beds may be repeated. The total length of the line from Rovey Head to 
Noss Head is 63 miles. On protracting a section from the measured angles of 
dip, taken while boating along the base of the cliffs, I find that if we make a 
liberal allowance for the effect of crumpling and dislocation, we shall still 
probably be within the truth in assigning a depth of about 5000 feet to what 
remains of the Old Red Sandstone of Shetland. 7 
2. Petrographical Characters and Order of Succession among the Strata.— 
The lowest visible strata occur on the mainland at Rovey Head, and consist 
of coarse conglomerate beds placed on end against the slates and limestones by 
the fault. So large are the blocks in these beds that we may reasonably 
infer that in spite of the fault they cannot lie far from the base of the.Old Red 
Sandstone of this district. The dislocation is probably not an extensive one, 
and at this part of its course seems to run nearly coincident with what was the 
actual margin. of the conglomerate area. With the conglomerates are inter- 
stratified bands of dark flagstone and grey sandstone. The north-easterly strike — 
of these lower beds carries them across the northern entrance of the Sound 
into the island of Bressay, the north-western promontories of which consist of 
reefs of very coarse conglomerate. As the strata ascend in the section they 
- become less conglomeratic, though pebbles still occur in them, either scattered 
irregularly or gathered into layers and nests. On the Score Head the grey 
sandstone besides its pebble-bands contains seams of dull red shale. At first 
the sandstones are somewhat thick bedded, but after passing Cullensbro’ 
Wick they assume the flaggy character which they retain through the rest of 
the section. The resemblance to the flags of the typical region of Caithness 
and Orkney increases as we round the precipices of Noss. When at last 
Rovey Head. Bressay. Noss Head. 

Fig. 9.—Section across the Old Red Sandstone of Shetland, from Rovey Head to Noss Head. 
we reach the stupendous Head, on the eastern front of that island, rising 
as a sheer wall 577 feet above the surface of the deep water which frets its base, 

