778 B. N. PEACH AND J. HORNE ON THE 
60. The Guactration of the SurttanD Istus. By B. N. Peacu, Esq., 
F.G.8., of the Geological Survey of Scotland, and Jonn Horne, 
Ksq., F.G.8., of the Geological Survey of Scotland. (Read 
March 26, 1879.) 
[Puare XXXIX.] 
ConrEnrTs. 
I. Introduction. 
Il. General Distribution of the Rock-formations. 
1. The metamorphic series. 
2. Intrusive igneous rocks older than the Old Red Sandstone. 
3. The Old Red Sandstone,—order of succession. 
4. Contemporaneous igneous rocks. 
5. Intrusive igneous rocks. 
III. Glaciation. 
IV. Boulder-clay. 
V. Morainic deposits belonging to the later glaciation. 
VI. Erratics. 
VII. Freshwater lochs and voes. 
VIII. Conclusion. 
1. Summary of the evidence regarding the primary glaciation. 
2. Insufficiency of icebergs or coast-ice to account for the pheno- 
mena. 
3. Shetland glaciated by Scandinavian ice. 
4. Absence of gravel kames and raised beaches in Shetland. 
I. Inrropucrion. 
One of the most interesting problems connected with glacial geology 
is the explanation of the glaciation of those groups of islands which 
lie at some distance from the north-east corner of the main- 
land of Scotland. It is now almost universally admitted, by those 
who have carefully weighed the evidence, that during the maximum 
cold of the glacial period, Scotland, Ireland, and the greater part of 
England were buried underneath an ice-sheet, which moved off the 
high grounds towards the sea-level. This has been clearly proved 
by the careful mapping of the ice-markings indicating the trend of 
the old glaciers, as well as by a minute examination of the stones 
in the Boulder-clay which accumulated underneath the ice, and was 
rolled along with the onward motion of the mass. So far most geo- 
logists are agreed; but when the glaciation of the Orkney and 
Shetland Isles has been discussed, it has given rise to considerable 
difference of opinion. Doubtless this want of uniformity has been 
largely due to the imperfect evidence hitherto obtained from the 
isles regarding the direction of glaciation and the nature of the 
various superficial accumulations. There has been no systematic ex- 
amination of Shetland, or even of Orkney, with a view to determine 
these questions ; and hence the absence of reliable observations has 
given scope for some latitude of opinion, and has lkewise retarded 
the final settlement of the question. 
The group of islands to which this paper especially refers may be 
said to form a broken rampart running nearly north and south for 
a distance of about 70 miles. The isles are about 200 miles distant 
