GLACIATION OF THE SHETLAND ISLES. 779 
from the Norwegian coast-line at Bergen, and about 86 miles from the 
north-east corner of Scotland. Though they are thus completely iso- 
lated from both countries, it will be shown that their physical history 
is to some extent associated with that of Scotland and Norway. 
The earliest references to the dispersion of boulders in these isles 
were made by Dr. Hibbert, who interred that “the great diluvial 
wave which swept over the low elevations of the whole of Scotland 
and England had in the latitude of Shetland a north-easterly origin, 
or, in other words, that it had a south-westerly direction” *. 
More recently certain observations on the glacial phenomena of 
Shetland were made by Mr. C. W. Peach, who visited Lerwick, the 
outskerries of Whalsey, and the island of Unst ; and at each of these 
localities he noted the ice-worn aspect of the rocks, the strie, and 
the existence of Boulder-clay tf. 
To our colleague, Dr. Croll, belongs the merit of having first sug- 
gested the probability of the North Sea being filled with ice, en- 
veloping alike the Orkney and Shetland groups of islands. This 
suggestion was first thrown out in a paper on ‘Glacial Submer- 
gence,” which appeared in the ‘ Reader’ of the 14th Oct. 1865. In 
a subsequent paper ‘‘On the Origin of the Caithness Boulder-clay”’ +, 
he pointed out that the Scandinavian and Scotch ice-sheets probably 
united on the floor of the North Sea, and thence moved northwards 
and northwestwards towards the Atlantic. He showed that in all 
probability the enormous mer de glace which pressed out on all sides 
from Scandinavia, produced, in virtue of its greater size, a slight de- 
flection of the Scotch ice, and caused it to override portions of the 
mainland. He indicated that in all likelihood both the Orkney and 
Shetland Isles were overtopped by the combined ice-sheets in their 
onward march towards the Atlantic. 
In the autumn of 1876, one of us visited Shetland with the view 
of determining the question whether the glaciation of that group of 
islands had any connexion with that of Scotland and Norway. From 
the traverses then made, it was evident that these isles had been 
glaciated by Scandinavian ice, though in certain areas it seemed as 
if a more recent local glaciation had well nigh effaced all traces of 
the original movement §. 
The rich variety of rocks in Shetland renders it a comparatively 
easy matter to determine the direction of the ice-movement; but in 
order to insure accuracy it seemed desirable to map out approxi- 
mately the areas of the respective rock-formations. During our 
leave of absence from official work in the summer of 1878, we there- 
fore returned to the isles for the purpose of accomplishing this end 
with as much minnteness as time would permit. We were induced 
* Edinb. Journ. of Science, vol. iv. pp. 85-91. 
+ Brit. Assoc. Report, 1864, p- 59. It should be remembered that Mr. C. W. 
Peach gives the magnetic rez rat | in his paper; and hence, in order to obtain 
the true direction of the ice-mar kings, due allowance must be made for the mag- 
netic deviation. 
{ Geol. Mag. vol. xvii. pp. 209 and 271. The fullest exposition of Dr. Croll’s 
views is given in ‘Climate and Time,’ chap. xxvii. 
§ Nature, vol. xy. p. 139. 
