154 GEOLOGY OF THE LOTHIANS. 



granite, that it is to be considered in circumstances which 

 are fitted for its undergoing a metamorphosis. It is not 

 enough to state that gneiss and mica-slate are metamorphic ; 

 but to prove that they are, it is necessary to find a mechani- 

 cal deposit becoming a gneiss or mica- slate. If an object 

 undergoes a metamorphosis, the fact of its having done so, 

 is only to be believed from the evidence of the senses in wit- 

 nessing the change, or from finding the original substance 

 in all states between a complete and an incipient alteration. 

 The junction of granite and greywacke at Loch Doon, 

 affords no support whatever to the doctrines to which we 

 have alluded, and certainly if such a theory is tenable, this 

 locality is one where we might expect to find appearances 

 in favour of it. On both sides of the loch, a junction of 

 the granite rocks with the greywacke is visible. On the 

 west side, however, these appearances are best exposed, and 

 we may remark that perhaps no part of Scotland exhibits, 

 in a more clear or marked manner, the connections of gra- 

 nite with stratified rocks. For many yards the junctions 

 of the two rocks are exposed in the most satisfactory man- 

 ner, veins of granite traversing the vertical greywacke strata 

 in all directions, and in some instances crossing them at 

 various angles with the planes of stratification, while in 

 others they run parallel with them. In breadth, the gra- 

 nite veins vary from six or seven feet to the smallest size, 

 and at their planes of contact with the greywacke, there is 

 in general an intimate commixture of both rocks, the 

 larger granite veins containing numerous variously sized im- 

 bedded angular fragments of the greywacke. The rocks 

 on the side of Loch Doon which exhibit the junction af- 

 ford every facility for examination, and from the action of 

 the water they are almost as smooth as if they had been po- 

 lished by art : the veins even of the smallest size may, 

 from their resisting the weather better than the greywacke, 



