The interpretation here briefly sketched differs widely from that arrived at by Professor Judd. The granitoid masses of the Red Mountains (Beinn Dearg) and the neighbouring heights are, in his view, the roots of the great volcano from which were erupted the various lavas; the earlier eruptions producing the acid lavas, to be followed by the gabbros, and these by the plateau-basaltic sheets, which stretch away towards the north and west into several peninsulas. Thus he holds that "the rocks of basic composition were ejected subsequently to those of the acid variety," and appeals to various sections in confirmation of this view.[3] To reconcile these views is at present impossible; but as the controversy between these two observers is probably not yet closed, there is room for hope that the true interpretation of the relations of these rocks to each other will ere long be fully established. [1] Geikie, _loc. cit._, p. 161, etc. [2] _Physical Geology of Ireland_, 2nd edition, p. 174 (Fig. 21). Professor Judd has also come to the conclusion that the granite of Mourne is of Tertiary age, _Quart. Jour. Geol. Soc._, vol. xxx. p. 275. [3] Judd, _loc. cit._, p. 254. CHAPTER V. THE SCUIR OF EIGG. Amongst the more remarkable of the smaller islets are those of Eigg, Rum, Canna, and Muck, lying between Mull on the south and Skye on the north, and undoubtedly at one time physically connected together. The Island of Eigg is especially remarkable for the fact, as stated by Geikie, that here we have the one solitary case of "a true superficial stream of acid lava--that of the Scuir of Eigg."[1] (Fig. 34.) This forms a sinuous ridge, composed of pitchstone of several kinds, of over two miles in length, rising from the midst of a tableland of bedded basalt and tuff to a height of 1,289 feet above the ocean; the plateau-basalt is traversed by basaltic dykes, ranging in a N.W.-S.E. direction. But what is specially remarkable is the evidence afforded by an examination of the course of the Scuir, that it follows the channel of an ancient river-valley, which has been hollowed out in the surface of the plateau. The course of this channel is indicated by the presence of a deposit of river-gravel, which in some places forms a sort of cushion between the base of the Scuir and the side of the channel. Over this gravel-bed the viscous pitchstone-lava appears to have flowed, taking possession of the river-channel, and also of the beds of several small tributary streams which flowed into the channel of the Scuir. The recent date of the pitchstone forming this remarkable mural ridge, once occupying the bed of a river-channel, is shown by the fact that the basaltic dykes which traverse the plateau-basalts are truncated by the river-gravel, which is, therefore, more recent; and, as we have seen, the pitchstone stream is more recent than the river-gravel. But at the time when this last volcanic eruption took place, the physical geography