in the neighbourhood of Loch Ness. 215 



pacter kind never assumes the rounded concretionary disposi- 

 tion incidental to most varieties of granite. 



The forms presented by the hills of quartz-rock, are con- 

 oidal, and in one or two instances serrated : the acclivities are 

 smoother than those which are found in mountains composed 

 of mica-slate or clay-slate, but they are bleak, and strewed 

 over with fragments. The conglomerated hills present more 

 undulating outlines, and their slopes are heaved up into rude 

 irregular precipices. 



The high mountain of Mealfourvoney, so often referred to, 

 exhihits on its summit a large dome or cupola of conglome- 

 rate, springing from a basis of the more compact quartz-rock. 

 This summit likewise sends off two very long waved ridges, 

 to the east and west, while its northern and southern sides 

 are formed into rugged mural precipices. 



4. Having thus described the detached characters of the 

 quartz-rock, its importance and geological position will now 

 be understood, by attending to its junctions with the other 

 rocks of the district ; and I shall next describe the quartz- 

 rock as it is found in junction with granite. 



This takes place on the south side of Loch Ness, especially 

 at the vitrified station of Dun-Jardil. 



There is no change produced on the quartz-rock in regard 

 to its chemical composition ; but some of the ingredients of 

 which it consists, increase in size, become visible to the naked 

 eye, and in many cases pass into a hard conglomerate, the por- 

 tions of which are sharp or angular, and partake more of a 

 form that is irregularly crystalline, than one which can be 

 considered as induced by abrasion. This appearance is occa- 

 sionally accompanied by the presence of large rhomboidal cry- 

 stals of felspar. The conglomerate here alluded to likewise 

 partakes of a mixture of the predominating colours of the 

 quartz-rock and granite. In other cases, however, the junc- 

 tion is marked hy the quartz-rock and granite alternating with, 

 or succeeding each other, in the form of irregular layers,— 

 the passage of one substance into the other being gradual, 

 and almost imperceptible. 



I have only further to remark, with regard to the relations 

 of these two rocks, that in certain places, especially on the 



