1858.] MUKCHISON NOETHEEN HIGHLANDS, ETC. 385 



rocks, limestones, mica-schists, (fee, would probably prove to be of 

 Silurian age. Fortunately the discoveries of Mr. C. Peach have 

 conclusively settled that question as respects one of their lower 

 members. 



A few observations are, however, called for in reference to a diffi- 

 culty which has presented itself to the mind of Professor Nicol. 

 Admitting, as he now does, that the quartzite group (which, from 

 mineral quahties, he had suggested might be of Carboniferous age), 

 is, as I supposed. Lower Silurian, he still doubts whether that group 

 really passes under the micaceous flaggy rock or eastern gneiss. His 

 doubts have been increased by finding, that along the line of junc- 

 tion there occur (particularly in the west of Eoss -shire, at the head 

 of Loch Maree) outbursts of igneous rock which he thinks are con- 

 nected with a general dislocation along the strike. 



But my observations do not support this view. See fig. 8 and its 

 appended Note. 



Such protrusions of igneous rock occur very irregularly in the 

 North-western Highlands and at various horizons. Thus we have 

 seen that in Canisp porphyry is associated with the lowest part of the 

 Cambrian rocks ; that hypersthenic rocks penetrate the limestones of 

 Durness and the quartz-rocks and limestones of Assynt ; that syenite 

 and felspar-rocks again reappear above the Silurian limestones at 

 Ledmore and on the banks of Loch Borrolan ; whilst the powerful 

 eruptive syenitic mass of Ben Laoghal penetrates the younger gneiss 

 in the heart of Sutherland. Such eruptions do not, therefore, in any 

 way specially cut off the fossiliferous Lower Silurian zone, but burst 

 through overlying strata of different ages. 



Compared, indeed, vdth the wide range of the stratified crystalline 

 rocks, these eruptive or igneous masses are mere pustules, which in 

 no wise derange the general succession, though they occasion partial 

 rolls and folds of the beds near the points of local intrusion. Thus, 

 in advancing to the S.E. from Assynt, we have no sooner passed the 

 boss of syenite near Loch Borrolan and the inn of Alt-na-GaUagach, 

 towards the E.S.E., than we are presented with the very same flaggy 

 micaceous succession which is so clearly exposed between Lochs 

 Eribol and Tongue. The eruptive matter is indeed very likely to 

 peer out here and there along the lines of least resistance, or where 

 one set of beds is overlaid by another. 



On the high road leading from the west to Lairg and the Dornoch 

 Firth, a limestone which I consider to be superior to any of the 

 Assynt rocks is exposed at Cnoc Craigie*. Though affording no 

 fossils under our hasty inspection, this rock, which is yellow and 

 apparently dolomitic, clearly overlies all the light-coloured quartzite 

 series, and is at once surmounted by dark-grey micaceous flagstones 

 quite unlike any stratum beneath them. At the Bridge of Alt EUag, 



* I was informed, by a very intelligent man who had accompanied the Sur- 

 veyor who made the map of Sutherland, that the Hmestone of Cnoc Craigie 

 reappears to the N.N.E. at Kinloch Ailsh and Fianloch More, at the west end of 

 Loch Shin ; and that freestone reoccurs in this flag -like series at Ben Skillachor, 

 north of Loch G-riam. 



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