CHAP. XXXVI 
STRUCTURES OF THE BASALTS 
19 
Fig. ‘260. — Banded amygdaloidal basalt 
showing layers of elongated anil steeply 
inclined vesicles. Macleod’s Maidens, 
Slcye. 
(fi) Where the banding arises from the distribution of the vesicles, somewhat 
similar weathered surfaces are produced. In some instances, while the basalt 
is throughout finely cellular, interposed bands of harder, rather finer-grained 
and less thoroughly vesicular character serve to give the stratified appearance. 
Instances may be observed where the vesicles have been crowded together in 
certain bands, which consequently weather 
out differently from the layers above and .vv>v. ST 
below them. An excellent illustration of 
this arrangement occurs in the lowest 
lava but one of the largest of the three 
picturesque stacks known as Macleod’s 
Maidens on the west coast of Skye (Figs. 
260, 283, 284 and 287). This lava is 
thoroughly amygdaloidal, but the vesicles 
are specially crowded together in certain 
parallel bands from an inch to three or four 
inches thick. Some of these layers lie close to each other, while elsewhere 
there may be a band of more close-grained, less vesicular material between 
them. But the most singular feature of the rock is to be seen in the shape 
and position of the vesicles that are crowded together in the cellular bands. 
Instead of being drawn out into flattened forms in the general direction of 
banding, they are placed together at high angles. Each layer remains 
parallel to the general bedding, but its vesicles are steeply inclined in one 
direction, which was doubtless that of the flow of the still unconsolidated 
lava. 1 Weathering along these bands, the lava might easily be mistaken at 
a little distance for a tuff or other stratified intercalation. 
Banded lavas possessing the characters now described are of frequent 
occurrence among the Inner Hebrides. Many striking examples of them 
may be seen along the west coast of Skye. Still more abundant in Faroe, 
they form one of the most conspicuous features in the geology of that group 
of islands. Along the whole of its western seaboard, on island after island, 
they are particularly prominent in the lower parts of the precipices, while 
the upper parts consist largely of amorphous or prismatic sheets. So much 
do they resemble stratified rocks that it was not until I had landed at 
various points that I could satisfy myself that they are really banded lavas. 2 
5 th. Ordinary flow-structure, save in these banded lavas, is rather rare 
among the plateaux. It may, however, be occasionally observed, where there 
is no distinct banding. On a weathered surface it appears in fine, widely 
parallel streaks, which are sometimes wavy, puckered and broken up, as in 
1 This elongation of vesicles, more or less perpendicular to the general bedding, may be noticed 
sometimes even in sills, as will be shown in a later Chapter. 
2 For recent contributions to the Geology of the Faroe Islands, see Prof. James Geikie, Trans. 
Roy. Soc. Edin. vol. xxx. (1880), p. 217, where the banding of the basalts is noticed ; Prof. A. 
Holland, Dansk. Geografisk. Tidskr. (1881) ; R. Breon, Notes pour servir a V etude dc la Otologic 
( lc V Islandc et des Isles Faeroe (1884) ; Mr. J. Lomas, True. Geol. Soc. Liverpool, vol. vii. (1895), p. 
292. Various writers have treated of the petrography of Faroe, particularly A. Osann, Newes 
Lahrb. (1884), vol. i. p. 45, and M. Breon in the volume here cited. 
