THE GEOLOGY OF THE FAROE ISLANDS, 226 
meet in the roof of the arcade where the beknotted mass projects downwards, 
reminding one of the groined ceiling of some Gothic structure. But the 
eccentricities of these dykes are endless, and no two are ever alike. They 
strongly reminded me of the irregular basalt-dykes and veins which occur so 
numerously in the Outer Hebrides.* 
There appear to be two systems of dykes, but they probably belong to the 
same age. One series trends from a little east of north to west of south, and 
the other from north of west to south of east; but the precise direction of 
some of those which we saw is not quite certain. When a dyke is only seen 
in one vertical sea-cliff section, and has not been traced inland, its true direc- 
tion may easily be mistaken, and such may quite well be the case with some 
which are indicated upon the map. Many of them, however, were so placed 
as to show their trend conspicuously enough, and these certainly gave evidence 
of a double series, one set running at approximately right angles to the other. 
But until the dykes in all the islands have been carefully mapped out this 
point will not be definitely settled. JI may remark in passing, that they are 
never so regular as the Miocene dykes in Scotland; these latter, as is well 
known, traverse the country in great wall-like sheets, from which often few or 
no subsidiary veins proceed; but the dykes of the Ferdes divide and subdivide 
again and again, and send out veins and threads innumerable. 
There is no evidence to show whether or not there is any connection 
between the dykes and the larger intrusive masses of prismatic basalt. It is 
quite possible, however, and even probable, that both belong to the same 
period of volcanic activity, and that they may have been injected from below 
at a time when sheets of basalt still continued to be poured out at the surface. 
LIV. THICKNESS OF THE STRATA: CONDITIONS UNDER WHICH THEY WERE 
AMASSED. 
1. Thickness of the Strata.—The dip of the basalt-rocks and tuffs in the 
northern islands, exclusive of Myggenzs, is somewhat persistently towards 
south-east, at an angle which hardly ever reaches 5°, and is usually much less. 
Sometimes, indeed, the dip is barely appreciable, and the beds appear to be 
quite horizontal. The average inclination certainly does not exceed 3°, but is 
probably greater than 2°. We have thus a thickness of 9000 or 10,000 feet 
for the rocks in the northern islands. To this must be added the thickness of 
the lower series (the beds under the coal) as developed in Myggenes, Suderée, 
and Munken, which cannot be less than 4000 feet. 
2. Igneous Rocks of Subaerial Origin.—Sir GEORGE MACKENZIE was of opinion 
that the “traps” of the Feerée Islands were the products of submarine volcanic 
* Quart. Journ. Geol. Soc., vol. xxxiv. p. 854. 
