﻿1861.] 



MTTRCHISON AND GEIKIE HIGHLANDS. 



185 



interstratified between the limestone and a higher micaceous series. 

 He has since endeavoured to invalidate his first impressions of the 

 locality, in order to support a theory subsequently embraced by him, 

 that what he called " upper gneiss " is really the lower Lau- 

 rentian rock brought up by a great dislocation. To favour this 

 explanation, he now lays stress upon the eruptive character of this 

 porphyry, and seeks to show that it has come up in a line of frac- 

 ture, carrying up with it the older gneiss. But for this hypothesis, 

 there is assiu-edly no foundation in the sections so well exposed 

 along the shores of Loch Broom. Prof. Kicol's first reading of the 

 geological sequence, from which he has since so widely departed, is 

 the correct one, and so palpable, indeed, that it coidd not easily be 

 missed. There are some features of this so-called " felspar -por- 

 phyry," however, which deserve special attention, since they bear 

 on the elucidation of the nature and process of the metamorphism 

 of the Scottish Highlands, and were carefully examined by one of us 

 along the sea-margin, the post-road, and the intervening ground. 



Where it overlies the limestone, it is a greenish, quartzose, ser- 

 pentinous rock. Tracing it clown to the shore and along the line 

 of low cliffs, we find the serpentine diminish in quantity, its place 

 being taken by pink felspar with a plentiful admixture of quartz- 

 granules. In this part of the rock, small rounded pebbles of red 

 jasper were observed; and a close scrutiny soon showed that such 

 pebbles, along with others of white and pink quartz, were abundant, 

 forming in some places about half of the rock. The weathered 

 surfaces, owing to the wasting away of the felspar, exhibited a 

 closely aggregated mass of small rounded granules of pink and 

 white quartz, which, in not a few instances, were arranged rudely 

 in rows like fines of stratification. Along the shore-line this rock 

 was found to become finer in grain, until it passed slowly into a 

 red sandstone, hardly distinguishable from that of the Cambrian 

 series, save in its paler colour and more metamorphosed aspect. 

 This sandstone is followed by a white quartz -rock very crystal- 

 line, and with no perceptible trace of bedding, though clearly itself 

 a bed between sheets of darker material. Above the quartz-rock 

 come greenish felspathic and serpentinous rocks with occasional 

 quartzose patches, the whole very irregular. These are succeeded 

 by a white and greenish serpentinous quartz-rock ; and beyond 

 this, the rocks, still serpentinous, shade off into quartzose flaggy 

 beds with a general south-easterly dip. These range south-eastward 

 for several miles with the same general inclination, and are in every 

 respect identical with the quartzose and schistose series already de- 

 scribed as overlying the limestone from Assynt to Loch Auchall. 



This intercalated band of so-called " felspar-porphyry " certainly 

 does not interfere with the regularity of the order of succession. 

 "We do not regard it as igneous at all, further than the gneiss is 

 igneous. On the contrary, the greater extent of alteration towards 

 the limestone, the larger amount of serpentine in the proximity of 

 that rock, the abundant rounded granules and pebbles of quartz 

 and jasper, the passing of the pebbly zone into sandstone, and of the 



