GLACIATION OF THE SHETLAND ISLES. 791 
varying, however, from 8.W. to 8. 15° W., the variation being due 
in many cases to inequalities of the ground; while on the south- 
eastern shore the trend varies from 8. 15° W. to 8. 28° W. Now it 
is apparent, on a moment’s consideration, that the direction of the 
striz would have been widely different had the island radiated its 
own ice, and had the glaciation been purely local. Both on the 
north-west and south-east shores the striz are either parallel with 
the long axis of the island or cut obliquely across it; and hence, in 
order to produce these striz, there must have been, during the 
primary glaciation, a mass of ice moving in that particular 
direction. 
In addition to this, there is evidence to prove that this island 
possessed local glaciers at a later period ; for to the north of Challi- 
setter ice-markings occur, trending N. and N.10° HK. Close by these 
later striations, numerous small moraines are seen on the gentle 
slope which flanks the central ridge in the northern portion of the 
island. 
There is, perhaps, no district in Shetland where the intense 
abrasion typical of glaciated regions is so patent asin the out- 
skerries of Whalsey. When sailing from the latter island to the 
Skerries, we were struck with the ice-worn aspect of the numerous 
little domes of rock projecting above the water. Housay, Brury, 
and Gruna may be described as large roches moutonnées which have 
been ground down, bared, and striated in a wonderful manner. 
From the top of the little hill south of the schoolhouse, one sees all 
round a succession of bare hummocks and domes of rock, destitute 
of any drift-covering, and with little vegetation, revealing un- 
mistakably the great pressure to which the islands have been sub- 
jected. In Gruna the strie vary from §.10° W. to W. 42°8.; in 
Brury, on the top of the highest hill, 8.35° W.; and in Housay, 
8.5.W. to S.W. 
A glance at the map will show that the instances now adduced 
coincide in direction with those occurring in Whalsey, and, with 
the exception of a little more southing, they agree with those 
in Unst, Fetlar, and en the east coast of Yell. In the case of the 
Skerries this south-westerly trend has a marked significance, inas- 
much as no one can possibly dispute that the glaciating agent must 
have been quite independent of the islets. It is equally clear that 
the markings are not due to the action of any local shect radiating 
from the Mainland of Shetland. Apart altogether from the fact that 
the position of the roches moutonnées, as well as a minute examination 
of the striated surfaces, convinced us that the ice crossed the Skerries 
from the north-east towards the south-west, there are other reasons 
why these markings cannot be attributed to any such local cause. 
When we come to discuss the evidence supplied by the Mainland in 
regard to the extent of the later glaciation, we shall see that there 
is satisfactory ground for maintaining that the later glaciers did not 
spread far beyond what is now the coast-line of that island. More- 
over, the direction of the later glacier movement on the east side of 
the Mainland is at variance with the trend of the strix occurring in 
