CHAP. XLIX 
DISLOCA TIONS OF THE PLA TEA UX 
453 
the west and a throw which may in some cases amount to about 20 or 25 
feet. The cumulative effect of this system of faulting, combined with a 
gentle westerly dip, is to bring down to the sea-level the upper band of con- 
glomerate which further to the east lies at the top of the clili. Again, the 
basalt-escarpment on the west side of Skye, from Dunvegan Head to Loch 
Eynort, is traversed by a series of small faults. On the east side ot Skye 
and in Kaasay, a number of faults, some of them having perhaps a throw of 
several hundred feet, has been mapped by Mr. H. B. Woodward. 
The largest dislocation observed by me among the basalt-plateaux ot the 
Inner Hebrides is that already referred to (p. 209), which runs at the back 
of the Morven outlier, in the west of Argyllshire, from the Sound of Mull 
by the head of Loch Aline to the mouth of Loch Sunart, along the 
line of valley that contains the salt-water fjord Loch Teacus and the fresh- 
water lakes Loch Durinemast and Loch Arienas. While the Cretaceous 
deposits and the bottom of their overlying basalts rise but little above the 
sea-level on the south-west side of this line, they are perched as outliers on 
hill-tops on the north-east side, where they rise to 1300 feet above the sea. 
The amount of vertical displacement here probably exceeds 1000 feet. The 
fault runs in a north-westerly direction, and has obviously been the guiding 
influence in the erosion of the broad and deep valley which marks its course 
at the surface. 
This dislocation is only the largest of a number by which the basalt- 
plateau has been broken in the district of Morven. Their effects are well 
shown in the outlier of basalt which caps Ben Iadain, where two parallel 
faults bring down the lavas against the platform of schists on which they 
lie (see Big. 266). 
Many faults have been traced in the Antrim plateau, and are represented 
on the Geological Survey Maps. In general they are of comparatively trifling 
displacement. Occasionally, however, they amount to several hundred teet, 
as in those already referred to as occurring near Ballycastle and around the 
southern part of the basin of Lough Neagh. 
To what extent the dislocations that traverse the British Tertiary 
basalts are to be regarded as comparable to those which in Iceland have 
been referred to subsidence caused by the tapping and outflow ot the lower 
still liquid parts of lava-sheets must be matter for further inquiry. So far 
as my own observations have yet gone, the faults do not seem explicable by 
any mere superficial action of the kind supposed. Where they descend 
through many hundreds of feet of successive sheets of basalt, and dislocate 
the Secondary formations underneath, they must obviously have been pro- 
duced by much more general and deep-seated causes. 
It is conceivable that, if these dislocations took place during the 
volcanic period, they broke up the lava-plains into sections, some of which 
sank down so as to leave a vertical wall at the surface on one side of the 
rent, or even to form open “gjas,” like those of Iceland. But it is note- 
worthy that the fissures, which have been filled with basalt and now appear 
as dykes, comparatively seldom show any displacement in the relative levels 
