796 B. N. PEACH AND J. HORNE ON THE 
thesis that the primary glaciation of the island was due to floating 
ice. 
If we traverse the southern shore from Muness Castle to Belmont, 
similar evidence is obtained from the Boulder-clay regarding the ice- 
carry. Again, in the north part of the island, in the lee of Saxavord 
hill, this deposit occurs on the east bank of Burra fiord, about 
300 feet above the sea-level, where it reaches 50 feet in depth. 
The material is mainly derived from the talce-schist and quartzose 
bands which constitute the hill; but a considerable proportion of 
the stones likewise consist of the peculiar granite of Lambaness. 
Now it must be borne in mind that, ere these granite-fragments 
could have reached this position along the path-line indicated by the 
strie, they must have been transported in the moraine profonde 
across the shoulder of Saxayord hill, where it attains a height of 
800 feet ; whereas none of the Lambaness granite occurs 7n situ at 
a greater height than 150 feet. 
On the west coast of Fetlar, blocks of gabbro and serpentine, de- 
rived from the centre of the island, occur in the Boulder-clay north 
and south of Burgh Hall; while striated fragments of the same 
rocks, from Unst, are found in this deposit on the north-east coast 
of Yell. We likewise observed smoothed fragments of gabbro from 
Fetlar in. this deposit on the east coast, between Mid Yell and Basta 
Voe. 
A traverse across the district of Northmavine, in the Mainland, 
from Ollaberry on the east coast, by Hillswick, Braewick, Tanwick, 
to the Grind of the Navir, furnishes admirable opportunities for 
examining the distribution of the stones in the Boulder-clay. <A 
glance at the map will show the variety of rock-formations which 
occur along this line; and the marked lithological characters of the 
rocks fortunately prevent any possibility of mistaking them. It is 
particularly observable that the till partakes of the physical character 
of the rock-formation on which it rests, though there is also a per- 
centage of foreign stones derived from localities which lay in the 
path of the ice-sheet. The distribution of the stones in the Boulder- 
clay along this line of section places beyond all doubt that the ice- 
sheet, as it impinged on the Mainland, moved in a W.S8.W. direction, 
and as it left the Mainland it veered round towards the N.W. and 
NENW? 
The sections in the neighbourhood of Ollaberry, and along the 
road to the Pondswater loch, show that the Boulder-clay is made up 
of the underlying gneissose and schistose rocks. The deposit consists 
of a stiff stony clay, containing fragments of schists, gneiss, and 
quartz rock. None of the fragments of the diorite, nor any of the 
lavas and ashes along the western shores, occur in the Boulder-clay. 
But when the diorite area is reached, the schists and gneiss to the 
east are represented in small patches of the deposit lying in hollows 
between the roches moutonnées. Beyond the diorite-area again, in 
the lee of the ridge of the metamorphic rocks of Hillswick, one of 
the finest Boulder-clay sections to be found in the Mainland occurs. 
This section, which is upwards of 100 feet in depth, rests on grey 
