[151] "On the Chronology of the Trap-rocks of Scotland," Trans. Roy. Soc. Edin. xxii. (1861), p. 649.
[152] Proc. Roy. Soc. Edin. vi. (1867), p. 71.
[153] Brit. Assoc. Report (Dundee), 1867, Sections, p. 49.
[154] Quart. Journ. Geol. Soc. xxvii. (1871), p. 279.
Three years later Mr. J. W. Judd read before the Geological Society a paper "On the Ancient Volcanoes of the Highlands."[155] The most novel feature of this paper was the announcement that the author had recognized the basal wrecks of five great central volcanoes in the Western Islands, among which that of Mull was inferred by him to have been at least 14,500 feet high. He was led to the conclusion that the volcanic period in these regions was divisible into three sections—the first marked by the outburst of acid rocks (felspathic 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 ("felspathic, basaltic, or intermediate in composition") after the great central cones had become extinct. It will be seen in the following pages that these conclusions of Professor Judd are not supported by a more detailed study of the region.
[155] Quart. Journ. Geol. Soc. xxx. (1874), p. 220.
In the year 1879, during a traverse of some portions of the volcanic region of Wyoming, Montana and Utah, I was vividly impressed by the identity of structure between the basaltic plateaux of these territories and the youngest volcanic areas of Britain. It then appeared to me that some of the puzzling features in the Tertiary volcanic series of the Inner Hebrides might be explained by the structures so admirably displayed in these lava-fields of the Far West.[156] Riding over the great basalt-plains of the Snake River and looking at the sections cut by the river through the thick series of horizontal basalt-beds, I appreciated for the first time the significance of Baron von Richthofen's views regarding "massive" or "fissure" eruptions, as contradistinguished from those of great central cones of the type of Etna or Vesuvius, and I gathered so many suggestions from my examination of these American regions that I renewed with increased interest the investigation of the Tertiary volcanic tracts of Britain. At last, after another interval of nine years, during which my weeks of leisure were given to the task, I was able to complete a discussion of the whole history of Tertiary volcanic action in this country, which was communicated to the Royal Society of Edinburgh in the early summer of 1888.[157] Since that time I have continued the research, and have from time to time communicated my results to the Geological Society. These various memoirs are combined with hitherto unpublished details in the following account of the British Tertiary Volcanic Rocks.
[156] Geological Essays at Home and Abroad (1882), pp. 271, 274; Nature, November 1880.
[157] Trans. Roy. Soc. Edin. vol. xxxv. part ii. (1888), pp. 23-184.
Professor Judd has also prosecuted the investigation of the petrography of the rocks, and has published his observations in the Quarterly Journal of the Geological Society.[158] To these papers by him more detailed reference will be made in later Chapters.