548 report — 1884. 



It must, however, be noted that elsewhere, as in this district, we find 

 intervening between these two series, either an interval of granitoid rock, 

 as in Glen Logan, or a fault cutting out a part of the supposed lower 

 series, as at the mouth of Glen Torridon. 



This granitoid rock (variously called syenite, diorite, granulite, &c.) 

 was by both the principal disputants, Murchison (with Geikie) and 

 Nichol, as at first by Hicks, considered to be an intrusive igneous rock, 

 to which the obscuration of the succession was mainly due. After a visit 

 in 1879 to the Loch Maree neighbourhood I pointed out that there were 

 none of the usual indications of the intrusion of a granitic rock, but every 

 indication of a faulted junction, and that lithologically the Logan rock 

 (as it has been called for purposes of reference) is inseparable from 

 the older part of the Hebrideau series, and often exhibits indications of 

 intense crushing. 1 This view is supported by specimens from Assynt 

 collected by Dr. Callaway, and from Eriboll, by Professor Lapworth and 

 others ; it is maintained by them, and is now accepted by Dr. Hicks.' 2 

 We have then to deal with the fact that between the eastern gneiss and 

 the quartzite-limestone group there is often an irregular wedge of the 

 old Hebridean floor, bounded on the one side by a fault whose throw is 

 equal to the whole series from the base of the Torridon sandstone 

 upwards (all the Cambrian and Ordovician), and on the other (according 

 to the Murchisonian hypothesis) by one somewhat greater. It has been 

 shown by Dr. Callaway and Professor Lapworth that a prolonged study 

 of the assumed sequence of the limestone or quartzite and the eastern 

 gneiss in the Dnrness and the Eriboll regions brings to light most serious 

 stratigraphical difficulties, and that the apparent conformities (where 

 they exist) are better explained by an overfold or overthrust in faulting. 3 



Further, all would admit that the great mass of the central High- 

 lands, wherever it has been studied (excluding some in-folded masses of 

 grit, quartzite, schistose and slaty beds, very probably Palosozoic), con- 

 sists of schists and gneisses corresponding very closely with those 

 typified by the rocks in the above-described section from Glen Logan 

 southwards, especially by the more highly altered or more southern 

 members of it. Now, dealing for a moment simply with the lithological 

 aspect of the question, it has been shown by Dr. Hicks 4 (and his view 

 is confirmed by Mr. T. Davies, and accords with my own studies of his 

 specimens) that rocks in the main agreeing with the upper portion of 

 the admitted Hebridean series predominate over a broad strip extending 

 in a NNE. direction from Loch Shiel and the head of Loch Eil ; that 

 on the south of this region, about the lower part of Loch Eil and the 

 southern part of the Caledonian Canal, rocks bearing a general resem- 

 blance to those of Ben Fyn,near Achnasheen, occur, and on the north of 

 it a district occupied by similar rocks extends inward from the western 

 coast about Arisaig to the north shore of Loch Carron ; this, crossing 

 the valley leading down to the sea so as to include Ben Fyn and the hills on 

 the north side, stretches northward to include the head of Glen Logan 

 and the region of Loch Fannich ; and, further, that similar rocks occur 

 at Gairloch, flanked on the eastern side by the Upper Hebridean, which 



1 Q. J. G. S., vol. xxxvi. p. 92. Nearly the same view had independently occurred 

 to Mr. Hudleston, Proc. Geol. Assoc, vol. vi. p. 75. 

 - Q. J. G. S., vol. xxxix. p. 143. 



8 Q. J. G. S., vol. xxxix. p. 355 ; Geol. Mag., Dec. ii., vol. x. 

 * Geol. Mag., Dec. ii., vol. vii. 



