While almost every week increases our knowledge of the geology of distant parts of the earth, there is one small island in the British seas, famed for its picturesque beauty, and peculiarly interesting on account of its historical associations, of the geological features of which very little is known, and even that little scarcely ever referred to in geological treatises. This may have arisen mainly from the fact of there having been as yet no official survey of this island; while those portions of the geological series represented in the Manx rocks having been typically established from other localities, it did not seem to present geological features sufficiently novel or peculiar to require any special investigation. Still, in the earlier years of the science, several eminent geologists did describe, with greater or less minuteness, some of its geological appearances: for example, Professor E. Forbes, who wrote a short account of Manx geology for one of the local guide-books; and a much more elaborate account was written by the Rev. J. G. Cumming, F.G.S., and published in 1848; but the rapid progress of the science, while it does not deprive these descriptions of all value, has in a great measure superseded them, and opened here a wide and almost untrodden field for the modern geologist. Having for several years resided on the island, and being convinced that many of the phenomena presented by the Manx rocks, if not altogether new to the geologist, are yet of remarkable interest, and capable of taking a great part in the solution of many of the problems which geologists are now endeavouring to solve, I have written the following brief account, with the view of diffusing, through the pages of the ‘Geologist,’ a more general knowledge of the geology of the Isle of Man, and in the hope of attracting to the subject that attention which it deserves.