IN THE NORTH-WEST HIGHLANDS OF SCOTLAND. 381 



to the investigation of the problem of the " newer gneiss." He had 

 at an early period recognized the possibility that this gneiss might 

 have been " forced over the quartzite ; " and this view he en- 

 deavoured to establish by the evidence of many natural sections. 

 He was ultimately led to maintain that the limestone is the highest 

 member of the Silurian series in that region, and that the so-called 

 " Upper Quartzite " and " Upper Limestone " of Murchison's sections 

 are merely the repetitions of the lower quartzite and limestone, 

 due to faults or folds. While admitting that in places the quartzite 

 and limestones are overlain by gneiss, he contended that there is 

 no conformable upward succession from the fossiliferous limestone 

 to the overlying schists and gneiss, but " that the line of junction 

 where this conformable succession is said to occur is clearly a line 

 of fault, everywhere indicated by proofs of fracture, contortion of 

 the strata, and powerful igneous action." The igneous rocks, which 

 he erroneously regarded as having been erupted simultaneously with 

 the displacement of the strata, were termed " granulite." Along 

 the line of fault, where the disturbance has been most violent, 

 Nicol further observed that the quartzite is " often much hardened 

 and semifused," though its fragmentary character is still recognizable. 

 From the foregoing data he inferred that the sections in the ISTorth- 

 west Highlands are but the counterpart of those in the Alps, where 

 crystalline rocks are seen resting on unaltered strata due to enor- 

 mous inversion and overthrow, and that a comparatively small 

 amount of inversion and extrusion of older crystalline masses will 

 suffice to explain any of the Scottish sections. 



With reference to the strike of the crystalline rocks, Nicol admitted 

 that in the western region the general trend is N.W., and in the 

 central areas N.E. ; but this distinction is not universal. He 

 ventured the suggestion that the gneiss of Scotland may belong 

 to distinct geological periods. Regarding the divergence in minera- 

 logical character between the western and eastern gneiss,he conceded 

 that hornblendic varieties of gneiss are very characteristic of this 

 formation in the west of Sutherland, but the more usual kinds also 

 occur; while, in the eastern district, he contended that rocks quite 

 as hornblendic and as thoroughly granitic in character are to be 

 found. In his opinion the peculiar character of the rock has no 

 relation to its age or locality, but to its proximity to the great 

 foci of igneous action. Near the granitic and syenitic eruptions 

 the gneiss appears in the more coarsely crystalline and hornblendic 

 forms *. 



* " On the Eed Sandstone and Conglomerate, and the superposed Quartz-rocks, 

 Limestones, and Gneiss of the North-west coast of Scotland," Quart. Journ. 

 Greol. Soc. vol xiii. p. 17. 



" On the Age and Relations of the Gneiss Eocks in the North of Scotland," 

 Rep. B. Assoc, for 18.58, see p. 96. 



" On the Relations of the Gneiss, Red Sandstone, and Quartzite in the North- 

 west Highlands/' Rep. B. Assoc, for 1859, see p. 119. 



" On the Structure of the North-west Highlands, and the Relations of the 

 Gneiss, Red Sandstone, and Quartzite of Sutherland and Ross-shire," Quart. 

 Journ. Geol. Soc. vol. xvii. p. 85. 



' The Geology and Scenery of the North of Scotland.' Edinb. 1866. 



