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OLD RED SANDSTONE OF WESTERN EUROPE. 449 
NOTE ON THE VOLCANIC ROCKS OF SHETLAND. 
(Added August 12, 1878.) 
During the summer of the present year, my colleagues, Messrs B. N. PEacu 
and JoHN Horne, have spent some weeks together in Shetland, chiefly studying 
the glacial geology of these northern islands. In the course of their investiga- 
tions they made some interesting observations on the volcanic rocks associated 
with the Old Red Sandstone in parts of Shetland which I had not visited. 
I am glad to be able to supplement my Memoir with the following notes from 
Mr Horne’s verbal communications and Mr PEAcn’s written memoranda :— 
East side of Shetland.—Necks of volcanic agglomerate pierce the sandstones 
‘on each side of Noss Sound. One on the Bressay side is irregular in form, 
about 230 yards in length by 50 in extreme breadth, sending fingers into the 
surrounding sandstones, which are shattered, discoloured, and baked to an 
extraordinary degree. The neck itself is occupied almost entirely with angular 
and sub-angular fragments of the altered sandstone (including blocks of great 
size, some of them several yards in diameter), set in a matrix of comminuted 
sandstone. The only lavaform material is that which forms a thin vesicular dyke, 
seen on south-west margin, and which m many places coats the walls of this 
neck with a crust a few inches in thickness. The neck on Noss presents the 
same general features. That these volcanic orifices belong to the period of the 
sandstones among which they occur, is shown by the occurrence of a bed of fine- 
grained volcanic tuff, intercalated among the sandstones on the north-east of 
Bressay. It is not more than 3 or 4 feet thick. 
West side of Shetland—The conjecture offered on p. 421 of the foregoing 
Memoir has been amply confirmed by my colleagues. They have found that 
the district stretching from the mouth of Ronas Voe to the head of Braewick 
| consists of a splendid series of lavas and tuffs, with a few intercalated beds of 
chocolate-coloured and grey flaggy sandstones. The lavas are of the same dark 
purplish-red and.greenish tints, crystalline to compact textures, and. prevailing 
amygdaloidal and slaggy characters which distinguish the lavas of the Old Red 
Sandstone of central Scotland. I shall describe their petrographical characters 
iM a succeeding part of this Memoir. Thick bands of coarse volcanic con- 
glomerate or tuff sometimes separate the sheets of lava, which in other instances 
lie directly upon each other without any fragmental intercalation. The cliffs 
at Ockren Head and the Grind of the Navir present magnificent sections of 
these interbedded lavas and conglomerates. ' 
The pink quartz-felsite (“ pink granite” of Htppert), which stretches over a 
‘considerable area on either side of Ronas Voe, seems to have been erupted 
during the volcanic period of the Old Red Sandstone, and not to belong to the 
bider metamorphism of the surrounding and underlying schists, gneisses, &e. 
WOL; XXVIII. PART II. ; 6A 
