206 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



is again succeeded by fine-grained, grey gneiss much contorted, but 

 dipping south-east, probably at a high angle. Still higher, beds of 

 quartzite appear, dipping at 10° to S. 47° E., and thus, though the 

 immediate junction is not seen, apparently unconformable to the 

 gneiss. In others of the surrounding hills the quartzite, readily 

 recognized by its white colour, also appeared to rest unconformably 

 on the grey gneiss, but I was prevented from determining this point 

 by further examination. 



About ten miles from Fort William, Glen Nevis is crossed by a 

 great ridge of rock, through which the river forces its way in a series 

 of narrow gorges and rugged cascades. This ridge must have been 

 cut through by the river in some very different condition of the 

 country, as the valley beyond it lies at a much lower level than its 

 summit, and opens out to the upper part of Glen Treig, by what 

 would be its natural drainage. Above this ridge a large branch of 

 the river enters from the south, forming a fine waterfall over an 

 overhanging cliff. In this place there is another interesting section, 

 represented generally in fig. 12, though from the incessant rain and 

 mist I was again prevented following out all its details. 



Fig. 12. — Section of the upper part of Glen Nevis. 

 n. s. 



Red Granite. Mica-slate. 



On the north-west is the granite dome of Ben Nevis, pierced by 

 the porphyry prism that forms the summit of the mountain. To this 

 succeeds a ridge of mica-slate, dipping at 70° to N. 47° W., and 

 thus apparently below Ben Nevis. Both in mineral character and 

 dip these beds correspond with the mica- slate seen in Glen Spean, 

 above the opening of Glen Roy. The valley forms an anticlinal, as 

 the strata on the other side dip about 45° to the south, and in the 

 higher part of the mountains appear to be again covered by the 

 quartzite. 



22. Glen Spean. — In Glen Spean, on the north side of Ben Nevis, 

 a similar series of rocks is seen, but with some diversity in the 

 details. In the lower part of this glen the mica- slate dips generally 

 to S. 50° E., and contains one or more beds of limestone, which are 

 quarried in some places, and is also intersected by veins of red 

 felspar-porphyry and granite. Near the mouth of Glen Hoy the 

 dip changes, and the mica-slate further up dips bb° or 60° to N. 

 50°-55° W. These beds appear to correspond to the mica-slate 

 seen in the upper part of Glen Nevis. Some of the lofty mountains, 

 however, on the south, towards Loch Treig, consist of gneiss, which J 



