396 c. callaway on the newer one1ssic 



Loch Ereiboll. 



The evidence for the overthrow or overthrust of the Eastern 

 Gneiss npon the Assynt series is even clearer here than in the 

 southern localities. The proof is indeed so distinct that nothing 

 but the hastiness of most previous workers can, I think, account for 

 their failure to perceive the true interpretation. Prof. Mcol, who 

 probably gave more time to the district than any of my predecessors, 

 saw more clearly into the structure of the region than his contem- 

 poraries ; and I am glad to be in a position, however humbly, to 

 vindicate his reputation. Erom a prolonged study of the district in 

 the summers of 1881 and 1882, 1 am able to supply much additional 

 evidence, and to correct some errors of interpretation into which he 

 fell. The chief of these misapprehensions has reference to the rock 

 which he called " granulite ; " and it will be well to clear up this 

 point before attacking the main question. 



A. The " Granulite " of Nicol a lower division of the Caledonian. 



Cunningham held that in Ben Arnaboll (Poll Ath-roinn), the 

 "Upper" Quartzite was conformably overlain by "gneiss;" and 

 Murchison confirms this view, except that he describes the upper 

 rock as " chloritic, talcose, and micaceous schists." I hold, with 

 Cunningham, that the rock is a true gneiss ; indeed I have rarely 

 seen a more typical gneiss ; but its exact lithological composition 

 has no material bearing on our inquiry. I concede to these authors 

 that the gneiss does overlie the quartzite, though I will not say 

 " conformably." Nicol also saw this overlie ; but he evaded the 

 difficulty by affirming that the whole of the upper series was an 

 intrusive rock which he called " granulite." 



This " granulite " not only forms the higher part of Ben Arnaboll, 

 but it is exposed to the breadth of over half a mile in the valley to 

 the south, up which the path to Arnaboll runs. Eor convenience we 

 will call this the Arnaboll valley. Nicol says that in this section the 

 " granulite " " throws off the strata on each side, and involves large 

 fragments of the mica slate, with the laminse turned in various 

 directions." Erom this reading I decidedly differ. The valley 

 shows a very clear section of bedded rock, the series ascending from 

 W. to E. At the west end, apparently overlying the "Upper" Quart- 

 zite, is a grey and pinkish granitoid gneiss, passing up into a con- 

 siderable thickness of rather massive gneiss, striped with folia of 

 hornblende and dark mica (JSTos. 64, 77, 78, pp. 415, 416). Towards 

 the east this rock grows lighter in colour, and the bedding becomes 

 thinner, till, about the water-parting between Lochs Emboli and 

 Hope, it passes up into the ordinary flaggy type. 



The Arnaboll gneiss bears some resemblance to Hebridean : indeed 

 Prof. Bonney, judging from hand-specimens only, refers it to that 

 formation. But field-work does not confirm this opinion. The 

 conformity of the Arnaboll rocks to the Hope series is seen in strike, 

 in dip, in the unbroken sequence, as observed on many lines of 

 section, and in the gradual transition in mineral and lithological 



