Ch. VI.] PRIMARY ROCKS. Ill 



shores. If the lines of direction are connected throughout, 

 it will be seen that they are curved ; and the reality of the 

 curvature is proved by its taking place, not only in the inter- 

 vals between these islands, but even in the isle of Luing itself. 

 This curvature, however, is not so great as to implicate all the 

 parallel strata ; as it is not found in the Garveloch Isles, which 

 lie immediately to the westward of Luing. Although the 

 direction of these schistose strata is thus constant, with certain 

 trifling exceptions, which must be rather viewed as temporary 

 undulations than as serious deviations from their general 

 course, the dip is in different places not only various in 

 quantity, but also reverse in position. In Gigha, it is to the 

 westward ; while it is to the eastward, not only in Isla and 

 Jura, but in all the northern isles. To whatever quarter, 

 however, the strata dip, the angle of inclination is seldom less 

 than 20, and rarely exceeds 60. Over a considerable tract 

 on the mainland the mica-slate and clay-slate series accom- 

 pany each other, alternating together, and exhibiting fre- 

 quent transitions which terminate upwards by the predomin- 

 ance of the clay-slate. These stratified rocks extend in one 

 belt from the easternmost point of Scotland to Bute, run- 

 ning N.E. and S.W., and dipping towards the east ; and 

 they are subject to no other deviation or irregularity, than 

 those slight undulations from which none of the Scottish 

 strata are exempt. Now these two series of slate are also 

 continued into Arran ; but their continuity is there inter- 

 rupted, for a certain space, by a mass of granite. They are 

 no longer parallel to each other, nor do their strata possess 

 the same direction or dip. Indeed, such is the apparent con- 

 fusion, that the dips cannot be exactly ascertained ; yet it is 

 evident, on comparing a great number, that the predominant 

 tendency of the whole is conformable to the surface of the 

 granite on all sides ; or, in other words, that the strata repose 

 on the mountain mass. And since the micaceous series pre- 

 vails on the south-western side of the granite, and the argil- 

 laceous on the north-eastern side, it is evident, that the strata 



