CHAP. XLII 
THE BASIC SILLS OF THE FAROE ISLES 
323 
is 
able distances, they may be seen sometimes to break across these, as 
strikingly shown in one of the great corries on the east side of Kuno. 
One of the most remarkable sills in the Faroe Islands is probably that 
which forms so prominent an object on the western cliffs of Stromo, at the 
entrance into the Vaago- 
fjord (Figs. 328, 329). 
It is prismatic in struc- 
ture, and where it runs 
along the face of the 
cliffs, parallel to the 
bedded basalts among 
which it has been in- 
truded, presents the 
familiar characters of 
such sheets. The preci- 
pice of which it forms a 
part is that which rises 
Fig. 328. — Sill traversing bedded Basalts, elifl's of Stromo, at 
entrance of Vaagofjord. 
The caves and notches shown at the bottom of the precipice mark the posi- 
tion of the vents represented in Figs. 311, 312, 313, 314. 
begins to 
above the row of volcanic vents already described. But it there 
ascend the cliffs obliquely across the basalts until it reaches the crest of the 
great wall of volcanic rock at a height of probably about 1000 feet above 
the waves. From the crest of the precipice the upward course of the sill 
is continued into the interior of the island. It pursues its way as a line 
of bold crag along the ridges of the plateau, gradually ascending till it forms 
the summit of one of the most prominent hills in the district (Fig. 329). 
Some .further idea of the enormous energy with which the. sills were 
injected may be formed from this example, where the eruptive materials 
followed neither the line of bedding nor a vertical fissure, but took an 
oblique course through the plateau -basalts for a vertical distance of prob- 
ably more than 1500 feet. 
V. GENERAL DEDUCTIONS REGARDING THE TERTIARY BASIC SILLS 
If we consider the facts which have now been adduced regarding the 
position and structure of the sills, we are led, I think, to regard these masses 
as certainly belonging to the history of the basalt-plateaux, but, on the 
whole, to a comparatively late part of it. They consist of essentially the 
same materials as the lavas that form these plateaux, though with the 
differences of structure which the conditions of their production would lead 
us naturally to expect. Where they occur in thick masses, which must 
obviously have cooled much more slowly at some depth beneath the surface 
than the comparatively thin sheets could do that were poured out above 
ground, they have assumed a far more largely crystalline texture than that 
of the superficial lavas. As a rule, we may say that the thicker the sill the 
coarser is its texture, while the thinnest sheets are the most close-grained. 
Sills are especially abundant about the base of the basaltic-plateaux. We 
may examine miles of the central and higher parts of the escarpments without 
