798 B. N. PEACH AND J. HORNE ON THE 
and across the high grounds to North Brae, indicates in an unmis- 
takable manner the direction of the ice-movement during the 
primary glaciation. In passing out of the Vidlon valley, across 
the watershed into Swining Voe, the eye readily fixes on a rocky 
ridge or, rather, a series of semi-detached roches moutonnées, which 
present their bare slopes to Vidlon Voe, in the lee of which lie weil- 
marked “ drums” of Boulder-clay, whose long axes coincide in 
direction with the trend of the striw. This deposit covers the 
whole of the gentle peat-covered slope which forms the eastern 
boundary of Swining Voe; and it contains numerous fragments of 
a band of nodular gneiss, which crosses Lunnasting in a north-and- 
south direction about midway between Lunna and Lunna Ness. 
But, further, the Boulder-clay in both the valleys draining into 
Swining Voe consists of a tough tenacious clay, full of striated 
stones, derived mainly from the underlying schists, quartzites, and 
dark hornblendic rocks ; and associated with these are fragments of 
the coarse gneiss of the promontory of Lunna and the nodular band 
already referred to. 
Now it is interesting to note that both in the Vidlon and Swining 
Voes, which lay across the path of the ice-sheet, the Boulder-clay is 
found to have the greatest development on the eastern shores; while 
the western slopes, which were exposed to the full sweep of the 
abrading agent, are finely moutonnées and striated, and well-nigh 
destitute of drift. But if we take the adjoining Colafirth and Dales 
Voes, which coincide very nearly with the direction of the ice- 
markings of the primary glaciation, we find well-marked Boulder- 
clay slopes on both sides of the sea-loch, indicating that the deposit 
was distributed more or less equally along the bottom and sides of 
the yalley. 
These features remind one very much of the familiar terraces of 
Boulder-clay in the high-lying valleys in the south of Scotland ; 
while the deposit itself is in all respects identical with the ordinary 
Scotch till. Indeed, whether we consider the resemblance in the 
mode of occurrence, or the character of the deposits in Scotland and 
the Shetland Isles, we cannot resist the conclusion that both have 
a similar origin. 
But even in the Dales and Colafirth Voes it would seem that the 
deposit steals further up the slopes, and attains a greater thickness 
on the north than on the south banks—a phenomenon which may 
be accounted for by the supposition that the ice, as it moved up the 
sea-lochs, had a greater erosive effect on the one seabank than the 
other. This supposition is confirmed by a glance at the striz-map, 
which shows that the markings are not quite coincident with the 
banks of the yoes, but cross the southern shores at a gentle angle. 
After crossing the Leas of Deal and descending the valley between 
the Duddon and Gallows hills towards Busta Voe, the boundary-line 
of the diorite is again crossed, when fragments of this rock are found 
abundantly both in the moraines and the underlying Boulder-clay. 
Not a single block of this rock, howeyer, is to be met with on the 
‘surface or in the drifts to the east of the boundary-line. 
