GLACIATION OF THE SHETLAND ISLES, 797 
raicaceous schists, with bands of quartz-rock, which are much broken 
up immediately underneath the Boulder-clay. ‘These rocks are 
intersected by dykes of pink quartz-felsite, which are well seen on. 
the beach at the base of the cliff. The deposit is very tough and 
clayey, and quite homogeneous from the top to the bottom of the 
section ; it is likewise quite unstratified, the stones being scattered 
through the clayey matrix in an irregular manner. The lower part 
of the section is mainly made up of the underlying rocks ; but about 
halfway up the section, a percentage of stones was taken which 
yielded the following results :— 
Diorite (in situ to the east of section) .. 71 per cent. 
Felsite and hornblendie porphyry .... 17 6 
Nie imine an ey NS Ath ital aPau cer cra 6 af 
Vein orthoclase felspar.............. 4 Se 
NSISVCSUDIT IE 2) 9y.05 as At Wee ree a ae tbe 1 - 
DenpeNbUMNe A Mk ie astute aioal teas ay 1 3s 
100 
It may seem strange that none of the underlying schists are 
represented in the above percentage; but it so happened that the 
stones we selected high up in the section averaged about 4 inches 
across. In another percentage of stones measuring about 2 inches 
across, the underlying schists number about 15 per cent. The 
prominent ingredient in this section is the diorite, which occurs to 
the east of Hillswick; but it ought to be remembered that not a 
single fragment of the lavas and ashes to the west are to be found 
in this deposit. 
About two miles to the west of the foregoing locality, in the 
north-east corner of Braewick Bay, a section of Boulder-clay, 
about 12 feet high, is exposed resting on the intrusive quartz-felsite, 
containing diorite, schist, and felsite stones; while still further west, 
within the limits of the contemporaneous volcanic rocks, sections of 
Boulder-clay occur in the bays of Tanwick and Stennis, the included 
stones being dull purplish porphyrite, blocks of tuff, quartz-felsite, 
schist, and diorite. Further, along the storm-swept cliffs of the 
Grind of the Nayir, a thin deposit is traceable containing the same 
ingredients as at the localities last mentioned. The diorite stones, 
however, are comparatively rare at the Grind of the Navir; in fact 
they gradually diminish in number in proportion to the distance from 
their parent source ; and the very same remark applics to the other 
ingredients. 
We traversed the south bank of Roeness Voe from the head of the 
sea-loch to Ockren Head, where similar phenomena were observed, 
viz. the invasion of the quartz-felsite area by the diorite stones, and 
the invasion of the area occupied by the porphyrites by the diorite 
and quartz-felsite stones. Indeed the evidence obtained along these 
lines of section completely refutes the theory that these north- 
westerly strize could haye been produced by ice coming from the 
North Atlantic. 
Another traverse, from Vidlon Yoo westwards by Swining Voe 
.J.G.S. No. 140. 3H 
