0')i the Geological Struct itre of the Highlands of Scotland. 37 



miniature canon (Plate X.,fig. 6), hewn by the mountain torrent out 

 of slightly inclined beds of quartzite. Crossing on to a pretty little 

 suspension bridge, thrown across the gorge by Mr. Fowler, c.e., 

 60 feet in width, we looked down on the bed of the stream below, 

 at a depth of 222 feet — that is, over three and a half times the 

 width of the chasm at the spot where spanned by the bridge. 

 We could follow with our eyes the chasm for a considerable 

 distance above and below the bridge — the sides bounded by nearly 

 vertical walls of quartzite, decorated with a natural growth of 

 ferns, shrubs, and climbing plants — to the rapids by which the 

 torrent descended from a loch situated higher up the glen. Look- 

 ing down the stream, the chasm could be followed for about a 

 mile before it opened out on the wide glen of Braemore. 



This miniature canon is itself situated in a much wider valley, 

 bounded by mountains of quartzite, and in excavating it the 

 stream has been facilitated in its operations by numerous nearly 

 vertical joints, represented in Plate X., fig. 6, traversing the beds of 

 quartzite in the direction of its course, as well as by smaller 

 joints and fissures crossing these at obtuse angles. 



On descending along the shore of Loch Broom, we observed the 

 horizontal beds of Cambrian sandstone, about 3,000 feet in thick- 

 ness, appearing from below the inclined beds of quartzite on the 

 southern banks ; and at the bridge of Ault Corry crossing a burn, 

 about a mile from Ullapool, we had an opportunity of examining 

 the " Assynt limestone," here only ten feet in thickness, for the 

 first time,(PlateX.,fig. 7).* Justoutsideof Ullapool we passedabluff, 

 showing the superposition of the lower quartzite on the red sand- 

 stone and conglomerate of the Cambrian formation, with a clear 

 unconformity in the stratification. We had thus in our first day's 

 journey made a transverse section of the Lower Silurian meta- 

 morphic series of the Northern Highlands. It seemed clear to us 

 that notwithstanding some slight fissures, some faulting, and 

 possibly local foldings or inversions, we had traversed a gradually 

 descending series of highly metamorphised beds of quartzite, 

 gneiss, and schist, down to less highly altered beds in contact 

 with the Cambrian, inasmuch as the Assynt limestone and the 

 associated shales and flagstones could scarcely be recognised as 

 having undergone metamorphic action. This was pointed out to 



* Murchison and Geikie, Quart. Journ. Geol. Soc, vol. xvii., p. 184. 



