548 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 13, 



the mica-slate and clayslate dip outwards, or south, in regular order. 

 In the centre of the country, in Perthshire, I observed several years 

 ago that the strata in the outer zone of the primary rocks seemed 

 *'in some places to have been completely reversed*." This view is 

 confirmed by some sections, by Mr. D. Sharpe, in the eighth volume 

 of the Journal of the Society (p. 127, &c.), in which the clayslate 

 is clearly shown in the same anomalous position. In two of these 

 sections, as at Stonehaven, a mass of trap intervenes between the 

 clayslate and the red sandstone, and in one instance Mr. Sharpe 

 ascribes to this igneous rock the peculiar position of the clay- 

 slate in relation to the mica-slate. Subsequently he seems disposed 

 to assume that "the trap-rock runs along the whole line of the 

 Highland border," in order to explain what he well describes as the 

 perplexing and apparently contradictory position of the slates (p. 130). 

 Though there are strong grounds for admitting the existence of this 

 more or less continuous line of trap, yet it does not seem sufficient 

 to explain the phsenomena. These appear to me to be not a 

 mere upturn of the clayslate, abutting against the mica-slate along 

 a line of fault, or changing its dip by a synclinal axis, as in Mr. 

 Sharpe' s sections, but a complete inversion of the series, with the 

 newer rock dipping under the older. Such an overturn of an enor- 

 mous mass of strata implies some far more powerful agent than the 

 small mass of trap seen along the junction, and one situated in another 

 region, or to the north, not to the south, of the inverted bedsf . 



In reference to the junction of the clayslate and red sandstone, the 

 present boundary-line appears to be the result of a great fault ele- 

 vating the region to the north. x\long this fault the various masses 

 of trap noted have burst out, and dykes of great extent, and approxi- 

 mately parallel, are known in many places in the red sandstone. 

 The small portion of materials which the northern mountains have 

 furnished to the sandstones and conglomerates at their base shows 

 that these mountains could not then have formed a line of coast 

 exposed to the action of the sea. In the south of Scotland where 

 the red sandstone rests horizontally on upturned Silurian strata, 

 which evidently formed dry land at the period, the old line of coast 

 may almost be traced by the rounded boulders or angular fragments 

 of Silurian rocks imbedded in the conglomerates. In this and other 

 parts of the north the conglomerates are not thus connected with 

 the primary strata ; and their chief components are derived from 

 other sources. This diversity of origin is strikingly shown by com- 

 paring the newer drift deposits covering the extremity of the Gram- 

 pians, and derived from their detritus, with the sandstones and 

 conglomerates at their base. Both are evidently similar formations, 

 deposited almost in the same place, though at widely distant epochs 

 in the earth's history ; but how very distinct are their mineral cha- 



* Geology of Scotland, p. 169. 



t The change in the mineral nature of the rock along these divisional planes 

 proves that they mark successive strata, and are not, as has been stated, planes 

 of cleavage. Although the foliation of the gneiss and mica-slate is, in general, 

 approximately parallel to the stratification, yet this is not always the case, and these 

 two well-marked and very distinct structures — stratification and foliation — ought 

 not to be confounded. — J. N., Oct. 13, 1855. 



