THE GEOLOGY OF THE FAROE ISLANDS. 265 
They are finely displayed in those of Waagée, Osterde, Sandde, Skuée, and 
Suderée, and I have no doubt that they have played a most important part in 
determining the trend of the coast-line where that faces the open ocean. In 
the quieter fiords the action of the sea, although frequently well-marked, is of 
course not so conspicuous. 
Basalt-dykes almost invariably give rise to caves. This is due not so much 
to the decomposition of the basalt (which is generally a harder and less easily 
decomposed rock than the bulk of the bedded strata) as to the minutely 
fissured or jointed character of the intruded rock. The dykes are traversed 
by many long joints parallel to their direction, and by innumerable cross joints, 
so that they fall an easy prey to frost and the battering of the waves (see 
Plate XIV. section fig. 14) One of the most beautiful dyke-caves is that to 
which I have already referred, the “ Hole under Kjetle” (Plate XV. fig. 16). 
From the fact that caves occur solely at the sea-level and are nowhere seen 
inland, we gather not only that they are of purely marine origin, but also that 
no part of the Ferde Islands has been submerged within any late geological 
period. We searched everywhere for evidence of the former presence of the 
sea, but failed to find the slightest proof that the islands were ever smaller 
than they are now. This is in keeping with what my brother and Messrs 
Horne and Peacu have observed in Orkney and Shetland, and with what I have 
noticed in the Outer Hebrides. The belief amongst the inhabitants, indeed, 
is that the land is sinking, but the facts mentioned by them in support of this 
view do not appear to be satisfactory. Thus the shallowing of Saxen Fiord 
might be entirely due to the action of the Saxen stream, aided by the tide 
itself. There are several considerations, however, which lead me to believe 
that the islanders are probably right in their conjecture. The present coast- 
line does not appear to me to be very old. Had it been of long standing I 
should have looked for more evidence of excessive marine erosion. We know 
that along the present coast-line of Scotland a terrace of marine erosion is 
frequently visible. Our land has stood so long at its present level, that the 
waves have cut back the cliffs for some distance, so that at low tide a platform 
or terrace of rock is more or less exposed at their base. Now the rocks of the 
Feerde Islands are being denuded much more rapidly than those parts of the 
Scottish coast-line to which I refer ; and had the land remained at its present 
level for any prolonged period, we might certainly have expected to meet with 
such rock-platforms in the Ferée Islands more or less abundantly. But the 
cliffs seem generally to shoot down at once into deep water, and only in a 
few places were sea-stacks in any number. A submerged rock-platform 
diversified with numerous stacks, some of which peer above the sea-level, 
occurs along the west coast of Suderée, but this is apparently the only island 
which is thus reef-fringed. And even these reefs are perhaps too deeply 
VOL, XXX. PART I. 2k 
