CHAP. XXXVI 
STRUCTURES OF THE BASALTS 
193 
persistence is in great measure deceptive. We can seldom follow the same 
bed with absolutely unbroken continuity for more than a mile or two. Even 
in the most favourable conditions, such as are afforded by a bare sea-cliff on 
which every sheet can be seen, there occur small faults, gullies where the 
rocks are for the time concealed, slopes of debris, and other failures of con- 
tinuity; while the rocks are generally so like each other, that on the further 
side of any such interruption, it is not always possible to make sure that we 
are still tracing the same bed of basalt which we may have been previously 
following. On the other hand, a careful examination of one of these great 
natural sections will usually supply us with proofs that, while the bedded 
character may continue well marked, the individual sheets die out, and are 
replaced by others of similar character. Cases may not infrequently be 
observed where the basalt of one sheet abruptly wedges out, and is replaced 
by that of another. Where both are of the same variety of rock, it requires 
close inspection to make out the difference between them ; but where one is 
a green, dull, earthy, amorphous amygdaloid, and the other is a compact. 
Fig. *261. — Termination of Basalt- beds, Carsaig, Mull. 
black, prismatic basalt, the contrast between the two beds can be recognized 
from a distance (Fig. 261). In the basaltic cliffs of the west coast of Skye, 
the really lenticular character of the flows can be well seen. I may 
especially cite the great headland south of Talisker Bay, already referred to, 
where, in the pile of nearly horizontal sheets, two beds may be seen to die 
out, one towards the north, the other towards the south. Further north, in 
the cliff of the Hoe of Duirinish, a similar structure presents itself. Along 
the coast-cliffs of Mull, Morveu and Ganna the same fact is clearly dis- 
played. Thus on the west side of the Sound of Mull the slopes above 
bishnish Bay show a group of basalts, which die out southward, and 
are overlapped by a younger group that has been poured over their ends. 
Such sections are best seen in the evening, when the grass-covered lavas 
show their successive sheets by their respective shadows, their individuality 
being lost in the full light of day. A more striking example occurs beyond 
the west end of Glen More in Midi, where one series of basalts has been 
tilted up, probably during some volcanic episode, and has had a younger 
series banked up against its edges. 
In Antrim also, remarkable evidence is presented of the rapid attenua- 
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