674 J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 



At a distance of only a few miles another fault of smaller dimen- 

 sions crosses the outlying mass of Beinn-y-Hattan. 



Apart, however, from the great dislocations, the effects of which, 

 as we have seen, are so clearly manifest in the Western Highlands, 

 it is evident that, wherever preserved from denudation, the basaltic 

 plateaux of Miocene lavas, with their foundations of Secondary 

 strata, have owed their survival in a very great degree to powerful 

 earth-movements which have taken place. In the case of the Skye 

 volcano only a sector of about 50 degrees has escaped removal by 

 denudation out of the vast circular area of lavas which doubtless 

 originally surrounded it on all sides. The isolated masses of Secon- 

 dary rocks, capped by lava, in Dun Can, Strathaird, and Eu-Geur, 

 with the plexus of dykes and sheets that intersect all the older 

 rock-masses of Strath and Sleat, bear witness in the strongest pos- 

 sible manner to the fact that the volcanic action extended equally on 

 all sides from the Cuilin and Eed Mountains of Skye. As was well 

 recognized, too, by Macculloch, Murchison, and Forbes, as well as by 

 later authors, the great lava-plateau forming all the northern part of 

 the island of Skye exhibits in itself very striking evidences of the 

 irregularities of the great earth-movements which have taken place 

 in the district. Thus, while on the eastern coast of Trotternish the 

 Secondary rocks are found in the cliff-sections up to 1000 feet above 

 the sea-level, on the western coast they only just make their appear- 

 ance at a few points at that level, and for the most part, indeed, are 

 concealed altogether by the Tertiary lavas. The same inclined posi- 

 tion of the lavas of the basaltic plateaux is quite as strikingly seen 

 in Raasay as in Skye. Of minor flexures and fractures which have 

 occurred in both districts since the ejection of the Tertiary volcanic 

 masses, the number is almost infinite, and the striking effect pro- 

 duced by them is sufficiently patent to every one who studies those 

 wonderful coast-sections. 



In Mull the plateaux of basaltic lava have apparently suffered less 

 from denudation than have those of Skye ; and this is the result of 

 that central subsidence which, as I have shown in a former paper, 

 has produced such marked effects in the case of that volcano ; but even 

 in Mull, that great breach in the lava-plateaux which constitutes the 

 Sound of Mull, their interruption by numerous sea-lochs, and their 

 total removal on the south and east sides of the igneous centre 

 speak very impressively indeed of the enormous amount of waste of 

 the Tertiary volcanic rocks and of the subjacent Secondary strata by 

 denudation. The same conclusion is very strikingly confirmed by 

 an examination of the isolated patches of the basaltic plateaux form- 

 ing the islands of Staff a and the Treshnish group, all of which have 

 doubtless been separated from Mull by post-Miocene denudation aided 

 by earth-movements. 



Most strongly do the causes of the preservation of these strata 

 make themselves felt in the case of that great line of fault which 

 forms the north-western boundary of the Mull plateaux, and in that 

 singular series of outliers of basaltic rocks forming the summits of 

 mountain-peaks in Morvern, and reserving beneath them those re- 



