1856.] NICOL — aUARTZITES, ETC. OF N.W. SCOTLAND. 3d 



laminated, blue or grey shales, full of carbonaceous, plant-like im- 

 pressions, and strongly impregnated with iron ; — and lastly, of blue 

 or grey limestones alternating with shales, and in some places black, 

 bituminous, and emitting a **fretid odour similar to tliat detected 

 in various mountain-limestone strata." Even the external features 

 of the fine cliff of Stronchrubie, with its beds of limestone, sandstone, 

 and trap, are entirely those of the coal-formation : whilst those of 

 the quartzites of Ben Spiannue and Loch Eriboll are just those of 

 the sandstones in the south of Scotland or north of England. Now 

 though the occurrence of one of these beds or groups alone — of a 

 red sandstone and conglomerate, of a white sandstone and shale, or 

 of grey and bituminous limestone — would furnish no strong indica- 

 tion of age, yet the coincidence of the whole three in their proper 

 order is a far more powerful argument. It seems highly improbable 

 that in such a limited region as Scotland there should have occurred 

 in the palaeozoic age two such complex series of deposits, so nearly 

 identical in mineral characters and order, and yet that they should 

 not be contemporaneous. 



The chief objection to assigning so recent a date to these quartzites 

 and limestones is the remarkable fact, that on the east they dip below 

 gneiss. Now the gneiss of the central region of Ross and Suther- 

 land, dipping, with few exceptions, continuously to the south-east, is 

 observed passing under the Old Red Sandstone of Ross-shire and 

 Caithness. This clearly appeared in three traverses of this region, 

 from the east to the west coast, which I made in company with Sir 

 R. Murchison in 1855, and is indeed admitted by the most com- 

 petent observers*. If, therefore, this gneiss, that overlies the 

 quartzites of the west coast, is truly a portion of the great formation 

 of the central regions which underlies the Devonian rocks on the east, 

 and has been originally deposited and metamorphosed in the place 

 where it occurs, it seems necessarily to throw the red sandstones and 

 quartzites of the west coast into a much earlier geological period, — 

 most probably into the Lower Silurian. This continuity of the over- 

 Ijdng gneiss of the west with the underlying gneiss of the east coast 

 has, however, not been established, and would indeed be a work of 

 great difficulty in such a wild and pathless country. In those parts 

 of Ross-shire, also, where the quartzite directly overlies gneiss, it 

 is evidently the lower gneiss of the same ag^ with that on the 

 west coast of Sutherland, that forms the surface. The fact also 

 of the overlying gneiss having been metamorphosed in situ, and not 

 pushed up over the quartzite, is one requiring further investiga- 

 tion. The occurrence of igneous rocks — syenitic porphyries or 

 serpentines, at many points along the line of union, seems to 

 indicate a fault. On the other hand, the great extent over which 

 this relation has been observed, of fifty or a hundred miles, is un- 

 favourable to the view that it is the result of a slip or convolution of 

 the beds. The quartzite also and the limestone have undergone 



* " It is generally, but not universally true, that the dip [of the gneiss] is to 

 the south-eastward." — MaccuUoch, Mem. on Geol. Map of Scotland, p. 63. See 

 also the dips laid down on Mr. Cunningham's Map of Sutherland. 



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