204 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



I have examined this neighbourhood repeatedly, returning to it 

 again and again in different years, many points in its structure still 

 appear very obscure. In the slate-quarries on the south shore of 

 Loch Leven, the principal division -planes dip at 65° to W. 28° S., 

 and a corresponding dip is seen in some of the other rocks in the 

 vicinity. This plane, however, I am inclined to believe, is, in the 

 slates, that of the cleavage, whilst the true bedding, though very 

 obscure, dips nearly east. Further up the loch, limestone is quarried, 

 but the dip is very obscure; and beyond it, towards the foot of 

 Glencoe, mica-slate is seen very highly undulated, but probably 

 dipping S.W. towards and below the clay-slate. The mountains 

 west of the slate-quarries consist of quartzite intermixed with gneiss, 

 mica-slate, and limestone, but I found the dips so variable that no 

 fair average could be deduced. This is not wonderful when account 

 is taken of the enormous protrusions, in this region, of igneous rocks 

 — granites, porphyries, and greenstones, of almost endless diversity 

 in mineral character and age. On the north side of Loch Leven 

 the clay-slate dips to S. 40°-50° E., but again probably on the 

 cleavage. Taken as a whole, this region seems too highly disturbed 

 to throw much light on the relations of the formations. This is 

 specially true of the quartzites, of which some portions at least 

 appear rather a binary granite of quartz with a little red orthoclase, 

 than a stratified rock. It prevails especially in the higher parts of 

 the mountains, where the narrow ridges, much steeper and scarcely 

 broader than the roof of a house, covered with the small loose 

 angular fragments among which no vegetation takes root, shine in 

 the sun almost like drifted snow. 



21. Fort William and Ben Nevis. — The vicinity of Fort William 

 and Ben Nevis also presents some interesting sections. The lowest 

 rock seen on the east side of the Great Glen is probably the gneiss 

 near Nevis Bridge, which dips at 60° to S. 10°-15° E., and runs 

 apparently under the granite of the mountain. The shore of Loch 

 Eil, south from Fort William, consists of mica- slate alternating with 

 clay-slate and talc-slate, and dipping generally at 60° or 70° to 

 S. 50°-55° E. In a few places the beds dip N.W., probably near a 

 fault or anticlinal axis, running nearly in the direction of the loch. 

 These beds pass north towards Ben Nevis, where, at the foot of the 

 mountain, similar slates dip 65° towards S. 57° E. below the granite, 

 but separated from it by veins of the black porphyry which forms 

 the centre prism of the mountain. This porphyry, as has long been 

 known, is the newer eruptive rock, not merely piercing the granite 

 in mass, but forming irregular branched veins through it* as in 

 fig. 10. Generally, however, the strata do not extend far north of 

 the Nevis River, the slope of the hill consisting of granite inter- 

 mixed with numerous veins of red and black porphyry. The south 



* Nicol's Geology of Scotland, p. 164. Here also I described the singular 

 brecciated character of this porphyry as shown on the weathered surface. So 

 marked is this character, that one is almost induced to speculate on the possibility 

 of this rock being a huge fragment of some old stratified deposit caught up in, 

 and metamorphosed by, the granite. 



