I860.] TnOST BB.EADALBANE MINES. 423 



not seldom, and in marked richness, surround fragments of the 

 greenstone. This probably arose from the fluid mass cooling sooner 

 in these places, so that the metallic minerals suspended in the por- 

 phyry adhered to and fastened themselves in greater abundance on 

 and near the cooler surfaces of the broken greenstone ; whilst the 

 main stream of the porphyry, loaded with the same minerals, con- 

 tinued its way, and both rock and mineral particles had 'to harden 

 together. During this process the particles of ore easily penetrated 

 the smallest crevices of the greenstone, where they soon cooled down 

 and solidified, as can be observed on innumerable specimens, and in 

 many varieties. 



Not only has the greenstone partaken, partly at least, of a change 

 as regards its absolute situation and its chemical composition, but 

 parts also of the mica-schist, though to a less extent and less fre- 

 quently. 



If mica-schist came in contact with the porphyry, the formation of 

 slickenslides or surfaces of friction took place. In the mines of 

 Tomnadashan several such divisions, which have received the general 

 name of " clay- veins/' may be seen, forming very regular courses 

 both in perpendicular and horizontal directions, They are of some 

 importance to the miner, because they are leaders through the hard- 

 ness of the rock to be opened, and they are receptacles of the more 

 valuable minerals, in the same way as the greenstone. 



Besides the above-mentioned metallic ores, carbonate of lime, in 

 scalenohcdron-macies and in other crystallographic combinations, as 

 well as dolomite, rpiartz, and sometimes sulphate of baryta, have 

 been found near the richer deposits of ore, especially where the grey 

 copper-ore predominates. 



Molybdenite is met with as an accessory mineral everywhere. In 

 all other respects the valuable minerals are deposited apparently in 

 a casual arrangement. 



Relation of the Valleys to the lines of fracture. — The same rocks, 

 greenstone and porphyry, appear in many other localities of the 

 valley of Loch Tay; and there is little doubt that to these igneous 

 masses the formation of the now water-covered valley itself is 



attributable. The same conclusion may lie drawn in reference to 

 Loch Awe, Loch Tulla, and Loch Ltivc, in the western ami north- 

 western pari "I' the district, where, however, granites and granitic 

 porphyries have produced the . ame results that the greenstones and 

 porphyries have effected at Loch Tay. It is thus probable also that 

 verj many valleys have received their forms from similar agencies. It, 

 is a remarkable fact, that the highest points of the Highlands, like 

 Ben Lawers, Ben More, Ben Nevis, Ben Lomond, Ben Conachan, and 

 many others of less height, have at their feet il"- deepest valleys, 

 w 1 1 i- 1 1 have become hikes. 



Ardtallanaig. — At Ardtallanaig, only a mile distant from the 

 above-mentioned mines, similar geologies] features reappear; ami 

 tin- mica-schist has been repeatedly intersected by igneous rot fes, 

 thereby rending asunder a vein or veins, a nd intermixing the frag- 

 ments from different masses, so that the constituent members have 



