GLACIATION OF THE SHETLAND ISLES. 801 
the gradual retreat of the great ice-sheet when this northern archi- 
pelago was no longer influenced by the ice-sheets of adjoining 
countries, but nourished a series of local glaciers which deposited 
their moraines as they shrank back into the hills. 
VY. Morarnic Deposits BELONGING To THE LATER GLACIATION. 
On referring to the strie-map, it will be seen that numerous 
instances occur along the east coast of the Mainland, from Lerwick 
to Dunrossness, running in a §.8.H., 8.H., and E.S8.E. direction, the 
trend being affected by certain local influences. Now, along this 
tract there is an irregular covering of a loose morainic deposit, passing 
into an ordinary Boulder-clay, resting on the areas of the Old Red 
Sandstone, and containing fragments of the schists from the Cliff 
Hills, along with the stones derived from the underlying formation. 
These sections are exposed on the shore between Lerwick and Rovey 
Head, in the Clickamin bay, Wick Sound, Gulberwick Bay, and in 
the Old-Red-Sandstone areas from Sandlodge to Boddom. After a 
careful examination of these sections, we felt convinced that 
the small fragments of blue and grey schists occurring in the 
Boulder-clay and morainic matter have been derived from the hills 
which extend from the Wart of Skewsburgh northwards by Scallo- 
way to Dales Voe. It has been already shown that these schists 
and clay-slates form the highest ground between Dunrossness and 
Dales Voe north of Lerwick; and the occurrence of fragments of 
these rocks in the drift along the eastern seaboard points merely to a 
local radiation of the ice, after the great mer de glace that overflowed 
Shetland had melted back and was no longer confluent with the 
small glaciers that lingered on during the later glaciation. 
That this is the explanation of the foregoing phenomena seems 
still more likely when we examine the eastern sea-board of North- 
mavine between Colifirth Voe and Fethaland Point. At certain 
localities, in the narrow strip occupied by the metamorphic rocks, 
we found similar deposits mainly made up of the débris of the 
underlying rocks, but likewise containing stones derived from the 
Roeness plateau. These sections occur on the north bank of Coli- 
firth Voe in the North-Rooe bay; and again round the Fethaland 
fishing-station and in the Sand Voe. Now from Colifirth Ness 
northwards to Calsta extends a well-marked ridge parallel with the 
Biurg range, against which the local glaciers abutted, which were 
shed from the Roeness plateau. A similar ridge runs from North- 
Rooe Bay to Fethaland, culminating in the Lanchestock hill (416 
feet). These ridges deflected the later glaciers, and caused them 
to mové southwards into Colifirth Voe, and northwards into North- 
Rooe Bay and Sand Voe. Here and there, however, where the ice 
must have been heaped up, it streamed across the lower portions of 
the ridge flanking the sea. From the configuration of the ground 
it is apparent that the Roeness plateau must have shed its largest 
glacier in the direction of North Rooe. Hence it follows that only 
at certain localities reached by the local glaciers are fragments of 
the quartz-porphyry to the west associated with the schists in the 
