42 Scientific Proceedings, Royal Dublin Society. 



way at Lairg. The road lay along the valley of the Laxford, and 

 by the banks of Loch Stack, Loch More, and Loch Shin, crossing 

 the low watershed under Ben Hee. As far as regards this journey 

 I have only to observe that we had an opportunity of observing 

 the general succession of the beds from the lower quartzite up- 

 wards through the limestone series, the upper quartzite, into the 

 metamorphic schists, and that, with occasional undulations in the 

 stratification, there appeared to be a continually ascending series 

 till we reached the granite of Lairg. Thus the results arrived at 

 in reference to the succession of the beds between Scourie and 

 Lairg were found to correspond with those arrived at by the 

 more southerly traverse between Garve and Ullapool. 



Do Pre-Cambrian beds re-appear in the Central Highlands ? 

 The question has been asked and answered in the affirmative by 

 some geologists, " Do the Laurentian (or pre-Cambrian) rocks 

 re-appear in the Central Highlands of Scotland after disappear- 

 ing below the Cambrian sandstones and Lower Silurian quartzites 

 of the western districts ? " As far as the observations which we 

 were enabled to make are calculated to throw light on the ques- 

 tion, I can only state my own impression, that the evidence is 

 against this view. Throughout the districts of Sutherland, Ross, 

 and Cromarty which we visited, it was clear that the Laurentian 

 beds must be buried at enormous depths underneath the Lower 

 Silurian beds the further we proceed eastwards from the outcrop. 

 It is quite possible that the whole of the Cambrian sandstones 

 may be absent under the centre of the North Highlands. From 

 the direction in which these rocks disappear through the effects of 

 denudation, it was evident that even at a short distance below 

 the upper quartzite they might be absent even when they 

 were in greatest thickness at the western outcrop. The sections 

 at Canisp and Quenaig are very suggestive of this. Therefore 

 we may well suppose that under the centre of the North High- 

 lands the Lower Silurian beds rest directly on a Laurentian floor ; 

 and it seems to me highly improbable (though possible) that these 

 latter rocks reappear at the surface, as there is clearly an 

 ascending series all the way from the west towards the east of 

 that part of Scotland. In the above statement I only refer to the 

 region north of the Caledonian canal. Until the geological sur- 

 vey of the Grampian range throughout the Inverness and Aber- 



