CHAP. XXXIII 
HISTORY OF INVESTIGATION 
I furnished evidence that this action was prolonged through a vast interval 
o time, during which great subaerial denudation of the older lavas took 
place before the outflow of the younger. 1 Later in the same year, in an 
address to the Geological Section of the British Association, I reiterated 
hese views, and more particularly emphasized the importance of the system 
°i dykes, which in my opinion was possibly the most striking manifestation 
of the vigour of Tertiary volcanic action. 2 * In 1871, after further explora- 
lons m the field, I gave a detailed account of the structure which had led 
to the mistake as to the age of the Tertiary volcanic rocks of the Western 
Islands ; and in a description of the island of Eigg, I brought forward data 
to show the enormous duration of the Tertiary volcanic period in the west 
of Britain. 
three years later Mr. J. W. Judd read before the Geological Society a 
paper “ On the Ancient Volcanoes of the Highlands.” 4 5 The most novel feature 
tllls P a P er was tlie announcement that the author had recognized the basal 
wrecks °f five great central volcanoes in the Western Islands, among which 
w,t of Mull was inferred by him to have been at least 14,500 feet hmh 
Me was led to the conclusion that the volcanic period in these regions was 
' ivisible into three sections— the first marked by the outburst of acid rocks 
def spathic lavas and ashes, connected with deeper and more central granitic 
masses) ; the second by the extrusion of basic lavas and tuffs (the basaltic 
Plateaux) ; the third by the appearance of small sporadic volcanic cones 
' tels pathic, basaltic, or intermediate in composition ”) after the great central 
.ones had become extinct. Tt will be seen in the following pages that these 
conclusions of Professor J udd are not supported by a more detailed study of 
•me region. J 
. In the T ear 18l79 > during a traverse of some portions of the volcanic 
°* w y° mill g> Montana and Utah, I was vividly impressed by the 
t mtity of structure between the basaltic plateaux of these territories and 
of Z° Unge , St vo ] camc areas of Britain. It then appeared to me that some 
P uzz Bng features m the Tertiary volcanic series of the Inner Hebrides 
field? ?r pl ; ime( ! by the structures 80 admirably displayed in these lava- 
Bivev ° I 1 ? , Far W<3St ' Eldm g over the great basalt-plains of the Snake 
of ]|(ii and looking- at the sections cut by the river through the thick series 
Baron JZ ° n ,a ^ desalt -beds, I appreciated for the first time the significance of 
as con tin v Jf lchth ° fe f’ s views regarding “ massive ” or “ fissure ” eruptions, 
or Vesi 18 Ulgms ied fr °m tliose of great central cones of the type of Etna 
these ? 1US ’ aUL 1 gathered so many suggestions from my examination of 
gatio? nf ei ? a V e8a0nS tlmt 1 renewed with increased interest the investi- 
interval nf ^ J ertlar y volcanic tracts of Britain. At last, after another 
o nine years, during which my weeks of leisure were given to the 
2 n ™/ ^ oy ' Soc ' Edi% - vi - (1867), p. 7i. 
2 a? ' Import (Dundee), 1867, Sections, p. 49. 
i °' rt ; J ° urn ■ Oeol. Soc. xxvii. (1871), p. 279. 
5 ij. Journ ‘ GeoL Soc. xxx. (1874), p. 220. 
60 ° (JWal Essa V s at Home and Abroad (1882), pp. 271, 274 ; Nature, November 1880. 
