GLACIATION OF THE SHETLAND ISLES. 803 
Tho scarcity of striz produced by the later glaciers in the district 
of Delting, when compared with their great abundance on the east- 
ern seaboard, near Lerwick, is deserving of note ; but their absence 
is doubtless due to the fact that the glaciers slipped forward over a 
terrace of Boulder-clay which effectually buried the underlying 
rocks, 
Abundant moraine heaps with enclosed tarns and innumerable 
blocs perchés were also observed between Colifirth and Sand Voes, 
and in the valleys draining into Roeness Voe, and likewise in the 
districts of Weesdale and Sandness. 
The islands of Unst, Yell, Whalsey, and Bressay nourished a 
similar series of local glaciers, as is evident from the moraines now 
strewn on their slopes. In the morainic deposit found on the north- 
western shore of Bressay, near Heogan, while the great majority 
of the stones consist of grits and liver-coloured quartz rocks belong- 
ing to the Old Red Sandstone, there is also a considerable number 
composed of grey schists, which we identified as belonging to the 
hills round the head of Dales Voe in the Mainland. This deposit 
resembles in every respect the sections occurring in the opposite side 
of the Sound near Grimmester, and again in the bays between 
Lerwick and Brenista. It is clear therefore that this deposit 
points to the advance of the local glaciers of the Mainland; they 
must have been powerful enough to cross the northern portion of 
the Sound, and to override the north-western part of Bressay. We 
searched carefully for traces of this more recent deposit in other 
parts of Bressay, but failed to discover them. The evidence in proof 
of the existence of local glaciers in the neighbourhood of the Wart 
at the south end of the island seems to indicate that their further 
advance would be checked on this account. We may well believe, 
therefore, that as the local glaciers of the Mainland streamed into 
the Sound, they were met by the small sheets of ice shed from the 
Wart, and thence moved southwards along the path of least resist- 
ance. 
VI. Enratics. 
From an examination of the numerous boulders scattered over 
the Mainland and the other islands, it is evident that their disper- 
sion belongs to two distinct periods of glaciation. We saw none 
which cannot be satisfactorily accounted for by the double system 
of #laciation already established, without invoking the aid of coast- 
ice or icebergs. 
Along the slopes of the Vallafield ridge in Unst we observed nu- 
merous blocks of serpentine, some of them measuring 5 feet across, 
which were dispersed during the primary glaciation. In the Main- 
land they occur in dozens on the rocky plateau of Roeness, on the 
diorite area north of Mayis Grind, and on the rocky headlands of 
Lunnasting. 
In the valleys draining the eastern slopes of the Rocness plateau, 
and in the low hills between Colifirth Voe and Fethaland, blocks of 
pink quartz-felsite are strewn, sometimes on the moraine heaps, cn 
