﻿I860.] 



XICOL N.W. HIGHLANDS. 



91 



Loch. Craggy passing below the limestone of Heilam Hill ; by the 

 same quartzite again rising up from below the limestone on the 

 coast near Tor-a-vu ; and by the fucoid-beds and limestone over- 

 lying it in regular order in several places south of the road to Loch 

 Hope Ferry. The occurrence of an upper qnartzite in this place is 

 thus not merely without proof, but contrary to many clear sections, 

 and, we shall soon find, has Ho support in any other locality*. 



The junction of the quartzite and mica-slate in the hills south of 

 our first section towards the head of Loch Emboli equally proves 

 that the mica-slate is the lower formation. In this place the 

 igneous rock has generally thinned out, or rather, instead of being 

 concentrated in a single mass or vein, becomes intermixed with the 

 lower mica- and talc-slates in innumerable fine threads or lines. 

 So intimate is this mixture, that, in many places, it is difficult 

 to say whether the rock should be classed as igneous or stratified. 

 Occasionally, however, larger masses occur, as near the road from 

 Emboli to Ault-na-harrow, where it forms a boss 50 to 100 yards in 

 diameter, and in the picturesque rock of Craig-na-feolin. Whether 

 concentrated in mass or dispersed in threads, the igneous matter is 

 far more abundant in the lower schists than in the quartzite, the 

 thick hard beds of the latter having apparently resisted its upward 

 progress and thus caused it to spread out in the inferior formation. 

 This distribution, therefore, of the igneous rock is another proof 

 that the eastern mica-slates are the lower formation, as, on the 

 supposition that the quartzite was the lower formation, it ought to 

 have been more powerfully invaded by the igneous rocks than the 

 schists resting upon it t. 



This intrusion of igneous matter, swelling out and expanding the 

 lower schists along the line of fault, has produced some complexity 

 in the sections. In many places the quartzites and mica-slate dip 

 approximately in the same direction, but are separated by a fault, 

 frequently marked by a low marshy hollow. A more interesting- 

 section is seen in a small stream above Emboli House (fig. 5). The 

 upper part of the ridge consists of talcose mica-slates (a) interlaced 

 with lines of red felspar. The dip near the top is 50°-60°, to E. 



* This hypothesis of an upper quartzite requires not merely the repetition of 

 the so-called " lower" quartzite with its characteristic annelid-tubes and peculiar 

 mineral characters, but also of a second group of fucoid-beds and a second lime- 

 stone, identical in order and character with those below ! But if such upper 

 beds exist, they ought then to have appeared in the Whiten Head sections, and 

 their absence is thus fatal to the notion of "conformable upward succession" 

 in this region. 



f These strata (chloritic, talcose, and micaceous schists), whatever may be their 

 mineral character, are riddled by the intrusive rock, and in parts much hardened 

 and altered." — Murchison, North Highlands, Quart, G-eol. Journ. vol. xvi. p. 235. 

 In p. 233 Sir R. I. Murchison describes them as "interwoven with the meta- 

 morphic Lower Silurian strata," i. e. with the eastern gneiss ; and also affirms 

 that "the granitic felstones and syenites so largely developed in the eastern parts 

 of Assynt .... rarely, if ever, occur between the limestones and the upper 

 quartz, but chiefly either in the latter or in the younger or overlying flagstones" 

 (p. 233). That is, aecording to my view, the igneous rocks are most abundant 

 in the crystalline schists beloiv, and in the quartzite where in contact with then. 



