116 



Mb. Brtce on the Geological Structure o/Roseneath. 



neons character, resembling a compact claystone or flinty slate, but still 

 enclosing crystals of mica. The laminje of the slate in contact with the 

 sides of the vein have a very close resemblance to this variety ; being, 

 in fact, a yellowish grey fine grained fliaty slate, with occasional spangles 

 of mica. It is thus difficult to determine the exact boundary line between 

 the slate and the vein. This assimilation of mineral character has 

 obviously been induced by the cooling of the masses from a state of 

 fusion, at nearly the same rate, but more rapidly than the inner portions 

 of the vein. The breadth of the vein is various ; in some places no more 

 than twelve or fifteen yards, in others as much as twenty-five, and even 

 thirty, and perhaps considerably above that, as it cannot in many cases 

 be exactly measured. It rises above the general surface of the hill side 

 from fifteen to forty feet in different places. 



6. The course which this erupted mass follows is indicated on the 

 accompanying map. In the northern part of its course it is interposed 

 as a bed between the strata of slate. To 

 the south of the high road, on the side of a 

 little stream, it is seen intersecting the beds 

 at a small angle, as in the annexed sketch. 

 No. 2, which is a vertical section. A little 

 farther south the ground rises considerably, 

 a a Mica slate, highly inclined, ^nd the vein ^ does not appear upon the 

 h h Plutonic rock intersecting surface ; the mica slate occupying the entire 

 the beds. space where it Ls possible the vein could 



appear ; but on the lowering of the ground still farther south, it again 

 emerges from beneath the slate and occupies the siu-face for some distance. 

 A similar overlapping occurs farther north, near the high road. Both of 

 these are expressed on the map. 



Though preserving a general N.N.E. and S.S.W. direction this vein 

 makes several undulations, throwing it a good deal out of its usual 

 course. The most remarkable of these is 

 seen not far from its northern termination, 

 and is represented in the annexed sketch, 

 No. 3, which is a ground plan. 



7. The appearance of this platonic rock, 

 now as a bed interposed among the strata, and 

 again as a vein intersecting them, and the 

 undulating course which it pursues, point out 

 its posterior origin and the nature of the 

 resisting force. This is plainly to be found 

 in the peculiar undulations and twisted forms 

 which everywhere characterise the mica slate, 

 indicating the powerful compressing forces 

 which acted upon it while yet plastic under 

 the influence of heat. 

 a a Vein of felspathic rock, about 25 yards wide, b b Melamorphic schist, 

 c c Common schiit in beds nearly vertical and parallel to tlic vein. 



