[317] Geology of Fife and the Lothians, 1839. More detailed reference will be made in later pages to this classic.
For many years I have devoted much time to the investigation of the Old Red Sandstone and its volcanic rocks. In the year 1859 I ascertained the existence of the great hiatus between the Lower and Upper divisions of the system.[318] A first sketch of the volcanic history of the Old Red Sandstone was given by me in 1861,[319] which was subsequently enlarged and filled in with more detail in 1879.[320] But it was not until 1892 that I published a somewhat detailed outline of the whole subject, tracing the history of volcanic action during the period of the Old Red Sandstone, the distribution of the volcanoes, and the character of the materials erupted by them.[321] This outline I now proceed to amplify, filling in details that were necessarily omitted before, though there are still several districts regarding which information is scanty.
[318] "On the Old Red Sandstone of the South of Scotland," Quart. Journ. Geol. Soc. xvi. (1860), p. 312.
[319] "On the Chronology of the Trap-Rocks of Scotland," Trans. Roy. Soc. Edin. vol. xxii. (1861), p. 63.
[320] Article "Geology," in Ninth Edition of the Encyclopædia Britannica, vol. x. (1879), p. 343. Reprinted in my Text-Book of Geology, of which the first edition appeared in 1882.
[321] "Presidential Address to the Geological Society," Quart. Journ. Geol. Soc. vol. xlviii. (1892).
In arranging the treatment of the subject I shall divide the record into two main sections, the first and much the more important being devoted to the Lower and the second to the Upper Old Red Sandstone. In the first of these divisions it will be convenient to begin by taking note of the distribution of the various districts over which the geological evidence is spread. We may then proceed to consider the general character of the volcanic rocks and the manner in which they are arranged in the stratigraphy of the country, taking in consecutive order (1) the superficial lavas and tuffs; (2) the vents; (3) the dykes and sills. From these general considerations we may pass to the detailed history of events in each of the separate volcanic areas, and thus obtain, as far as the evidence at present permits, a broad view of the progress of volcanic action during the time of the Lower Old Red Sandstone in Britain.
CHAPTER XVII
DISTRIBUTION OF THE VOLCANIC CENTRES IN THE LOWER OLD RED SANDSTONE—CHARACTERS OF THE MATERIALS ERUPTED BY THE VOLCANOES
i. DISTRIBUTION OF VOLCANIC CENTRES