Rising from the middle of the Irish Sea, within sight of each of the three kingdoms, with a history and associations so distinct, yet so intimately linked with those of the rest of Britain, this interesting island presents in its geological structure features that connect it alike with England, Scotland and Ireland, while at the same time it retains a marked individuality in regard to some of the rocks that form its framework. Its great central ridge of grits and slates, which still rises 2000 feet above the sea in the summit of Snaefell, must have formed a tract of dry land in Carboniferous time, until it sank under sea-level, and was buried beneath the Carboniferous and later formations. Along the southern margin of this ancient land, a relic of the floor of the Carboniferous sea has been preserved in a small basin of Carboniferous Limestone which covers about seven or eight square miles. This remnant has a special interest in geological history, for it has preserved the records of a series of volcanic eruptions which took place contemporaneously with the deposition of the Carboniferous Limestone. The geology of the Isle of Man was sketched in outline by J. F. Berger,[48] J. Macculloch,[49] and J. S. Henslow,[50] and was afterwards more fully illustrated by J. G. Cumming.[51] To the last-named observer we owe the recognition of true intercalated volcanic rocks among the calcareous formations of the southern end of the island. These rocks have subsequently been studied in greater detail by a number of geologists. An excellent general account of them was published in 1874 by Mr. John Horne, of the Geological Survey.[52] A few years later some further observations on them were prepared by J. Clifton Ward.[53] More recently their petrography has been studied by Messrs. E. Dickson, P. Holland and F. Rutley,[54] and in more detail by Mr. B. Hobson.[55] To some of the observations of these writers reference will be made in the succeeding pages. During the progress of the Geological Survey in the Isle of Man, the rocks in question have been mapped in detail by Mr. A. Strahan and Mr. G. W. Lamplugh, and I have had an opportunity of examining the coast-sections with the last-named geologist. The following description of these sections is taken mainly from my field note-book. The full details will appear in the official _Memoirs_. [Footnote 48: _Trans. Geol. Soc._ 1st ser. vol. ii. (1814), p. 29.] [Footnote 49: _Western Islands of Scotland_ (1819), vol. ii. p. 571.] [Footnote 50: _Trans. Geol. Soc._ 1st ser. vol. v. (1821), p. 482.] [Footnote 51: _The Isle of Man_ (1848), chap. x.] [Footnote 52: _Trans. Geol. Soc. Edin._ ii. (1874), p. 332.] [Footnote 53: _Geol. Mag._ 1880, p. 4.] [Footnote 54: _Proc. Liverpool Geol. Soc._ vol. vi. (1888-89), p. 123.]