(_c._) _Representative Rocks of Mourne and Carlingford, Ireland._--Assuming Sir A. Geikie's view to be correct, it is possible that we may have in the granite and quartz-porphyries of Mourne and Carlingford representatives of the granites, granophyres, and other acid rocks of the later period of Mull. The granite of Mourne is peculiar in structure, and differs from the ordinary type of that rock in which the silica forms the ground mass. In the case of the granite of the Mourne Mountains, the rock consists of a crystalline granular aggregate of orthoclase, albite, smoke-quartz, and mica; it is also full of drusy cavities, in which the various minerals crystallise out in very perfect form. As far as regards direct evidence, the age of this rock can only be stated to be post-Carboniferous, and earlier than certain Tertiary basaltic dykes by which it is traversed. The granophyres of Mull are traversed by similar dykes, which are representatives of the very latest stage of volcanic action in the British Islands. The author is therefore inclined to concur with Sir A. Geikie in assigning to the granite of the Mourne Mountains, and the representative felsitic rocks of the Carlingford Mountains, a Tertiary age--in which case the analogy between the volcanic phenomena of the Inner Hebrides and of the North-east of Ireland would seem to be complete.[5] [1] Geikie, _Proc. Roy. Soc. Edinburgh_ (1867); _Brit. Assoc. Rep._ (Dundee, 1867); "Tertiary Volcanic Rocks of the British Isles," _Quart. Journ. Geol. Soc._, vol. xxvii. p. 279; also, "History of Volcanic Action in British Isles," _Trans. Roy. Soc. Edin._ (1888); Judd, "On the Ancient Volcanoes of the Highlands," etc., _Quart. Journ. Geol. Soc._, vol. xxx. p. 233; and _Volcanoes_, p. 139. [2] _Brit. Assoc. Rep._ for 1850, p. 70. [3] Judd, _Quart. Jour. Geol. Soc._, vol. xxx. p. 242. [4] _History of Volcanic Action, etc._, _loc. cit._ p. 153, _et seq._ The "Granophyres" of Geikie come under the head of "Felsites," passing into "granite" in one direction and quartz-trachyte in another, according to Judd; the proportion of silica from 69 to 75 per cent.--_Quart. Jour. Geol. Soc._, vol. xxx. p. 235. [5] This view the author has expressed in a recent edition of _The Physical Geology of Ireland_, p. 177 (1891). CHAPTER IV. ISLE OF SKYE.