CHAP. L 
EFFECTS OF DENUDA TION 
459 
the east side of Yidero, across Boro to the centre of Ostero, and thence by 
the Sund across Stromo and Vaago. From this line the fjords and valleys 
diverge towards the north-west and south-east. There can hardly he any 
doubt that on the whole this line corresponds with the general trend of the 
water-parting at the time when tire Tertiary streams were flowing over the 
still continuous volcanic plain. Considerable depression of the whole region 
has since then sent the sea up the lower and wider valleys, converting them 
into fjords, and isolating their intervening ridges into islands. 
The topography of the Faroe Islands seems to me eminently deserving 
of careful study in the light of its geological origin. There is assuredly no 
other region in Europe where the interesting problems presented by this 
subject could he studied so easily, where the geological structure is through- 
out so simpfle, where the combined influences of the atmosphere and ot the 
sea could he so admirably worked out and distinguished, and where the 
imagination, kindled to enthusiasm by the contemplation of noble scenery, 
could be so constantly and imperiously controlled by the accurate observation 
of ascertainable fact. 
2. Impressive and easily comprehended as are the proofs of denudation 
supplied by the basalts of the plateaux, they are perhaps to a geological eye 
less overwhelming than those furnished by the eruptive rocks which have 
been injected into these plateaux. In the case of at least the basic intru- 
sions, we may reasonably infer that they assumed their present position 
under a greater or less depth of overlying rock which has since been 
removed. When, therefore, they are found at or above the summits ol the 
plateaux, they demonstrate that a vast amount of material has been removed 
from these summits. 
The argument from the position of the dykes has already been enforced. 
It is absolutely certain that valleys several thousand feet deep must have 
been excavated since these dykes were erupted, for had such valleys existed 
at the time when the dykes were injected across their site, the molten rock, 
instead of ascending to the tops of the surrounding mountains, would 
obviously have rushed forth over the valley-bottoms. I have shown that 
this reasoning applies not merely to the volcanic districts, but to the whole 
surface of the country within the region of dykes. Thus the uplands of 
Southern Scotland, and wide areas in the Southern and Western Highlands, 
can be proved to have had glens cut out of their mass to a depth ot 
hundreds of feet since the Tertiary volcanic period. 
Not less convincing is the evidence afforded by the great eruptive masses 
of gabbro. We have seen that these complex accumulations of sills, dykes, 
and bosses include rocks so coarse in grain as to show that they must have 
consolidated at some considerable depth, but that they now appear in hill- 
croups 2000 to 3000 feet in height, the whole of the original basaltic cover 
having been stripped off from them. But these gabbro hills have been in 
turn traversed up to the very crests by later basalt- dykes, which thus 
supply additional proof that the erosion here has been stupendous. 
The granophyre bosses tell the same tale. Though, like the domite 
