14 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 18, 



we have again the deeper red-coloured clays, indicating the vicinity 

 of the lower beds of the same series ; thence proceeding westward we 

 get clays of a dirty leaden hue, obtained from the flagstones and fish 

 bed of the middle series ; and still further westward we have a return 

 to the red colour, when it is found that the lower old red conglo- 

 merate is tilted up and reclines against the flanks of Ben Wy\ds. 



The constancy of this same current through a very lengthened 

 period is a most remarkable fact, and points to one simple agent at 

 work in the transportal of materials during the whole epoch of the 

 sinking and rising again of the land. 



There is every evidence that the materials of the drift-gravel plat- 

 forms, (which I believe to have been in greater part formed out of 

 the older boulder deposit during emergence,) as well as the larger 

 boulders on it, have been carried forw^ard still in the same direction. 

 I am not aware that any of these materials have anywhere been 

 discovered in situ to the eastward of their present localities. Accord- 

 ing to Mr. Anderson's testimony, whose accuracy of observation is 

 most remarkable, masses of a rather peculiar gneiss existing i?i situ 

 near the western shores of Ross-shire, are scattered eastward as far as 

 Tain and Tarbet Ness ; and the beautiful red porphpdtic granite of 

 Calder and Ardclach, between the rivers Nairn and Finclhorn, has 

 been borne eastward as far as Focbabers and Speym.outh. 



The existence of the gravel terraces to which I have just alluded, 

 is a very valuable evidence of the extent to which at least the land 

 has been submerged. 



For I think there is little reason why we should not attribute to 

 one and the same canse the terraces occurring along the Great Glen, 

 and in those which branch out of it, as Glen Spean, Glen Gloy and 

 Glen Roy, at all the various elevations at which they have been noted. 

 Now we have evidence that the most distinctly-marked terrace of the 

 Great Glen (that which in fact forms its summit-level or water- 

 shed at a height of about 100 feet above the present high-water 

 mark) is the remains of a sea-bottom. This remarkable terrace 

 commences at Laggan, betwixt Loch Oich and Loch Lochy ; thence 

 it runs along on either side of the Glen in the direction of the Moray 

 Firth. On the western side we find fragments of it, wherever a 

 resting-place is admitted by the otherwise precipitous wall of the 

 valley. It courses round by Ciacknaharry into the Beauly Firth ; 

 here we see it as a distinct fringe running far up into the country, 

 and after a circuit of about thirty miles, returning again on the other 

 side of the Firth to the Ord of Kessock. Thence we trace it in patches 

 down the north-western shore of the Moray Firth ; it runs into ^lun- 

 lochy Bay, and spreads out into a plateau betwixt Fortrose and Rose- 

 markie ; we follow it into Cromarty Firth, and thence round again 

 into the Dornoch Firth, and along the whole coast of Sutherland to 

 the Ord and bluff rocky shores of Caithness. It is however on the 

 south-eastern side of the Moray Firth that its true character as an 

 ancient sea-bottom is more distinctly developed. In the neighbour- 

 hood of Inverness, where the great valley begins to open out, and the 

 hills of the old red sandstone recede further into the countr\^ it 



