218 PBOCEEDINGS OF THE GEOLOGICAL SGCIETT. [Nov. 16, 



ing at the prevalent inclination of this older gneiss, we find that it 

 is usually to the west, whilst the overlying rocks in question, extend- 

 ing over enormous areas, dip everywhere to the east (fig. 2). Pass- 

 ing over the red and chocolate-coloured Cambrian sandstone (b), we 

 find that the first succeeding quartz-rocks and limestone (c), as well 

 as the next overlying micaceous schists and gneissose strata (d), 

 have a prevalent N.N.E. and S.S.W. strike (deviating, it is true, 

 to the ~N. and S., but never assuming the direction of the old or 

 fundamental gneiss), and with a determined prevalent dip to the east. 

 Looking to this fact, and to the clear order of superposition (as 

 expressed in the general section, fig. 2), and to a decided mineral 

 distinction between the true bottom-rock (a) and all the strata which 

 overlie them to the east, the hypothetical suggestion thrown out by 

 Prof. Nicol at the meeting of the British Association at Aberdeen, 

 that the eastern or gneissose and micaceous rock may be simply the 

 older gneiss exposed by denudations or brought up by faults, cannot, 

 in my opinion, be entertained. This point will presently be illus- 

 trated by fresh sections, when, having treated of the fossiliferous 

 Lower Silurian (c), we come to those crystalline mica-schists and 

 quasi-gneissose strata (d) which repose upon them. 



In the mean time I may state that, after carefully examining the 

 fundamental gneiss from Loch Inver to Durness, and then imme- 

 diately contrasting it with the upper micaceous and gneissose strata, 

 Prof. Ramsay and myself were quite as much struck with the great 

 lithological dissimilarity of structure and the different direction 

 of the two sets of rocks, as we are prepared to prove, by distinct 

 natural evidences in the field, that they are widely separated from 

 each other by an unquestionable order of superposition, and can never 

 be merged under the same colour and represented by the same letter, 

 as they have been in all previous geological maps of Scotland. Let 

 any geologist traverse, for example, the Kyles of Strom, on the west 

 coast of Sutherland, and there examine all the highly crystalline, 

 ponderous, grey gneiss, extending to Scourie and Loch Stack, or 

 view the grand development of the same rock, with huge granitic 

 intrusions, on the shores of Loch Laxford, where it forms the base 

 of the Fionavin range of quartz-rock, and its extension into Ben 

 Spionnach, and then contrast that subjacent rock with the mica- 

 ceous flaggy strata lying to the east of Assynt, Loch More, and Loch 

 Eriboll, and he will, I doubt not, arrive at the conclusion maintained 

 in my previous memoirs. 



Cambrian Rocks of the North-west Coast. — I have no modification 

 to make in what has been already stated respecting these rocks, but 

 would merely enlarge upon certain details respecting them. Thus, 

 in referring to the pictorial frontispiece at the head of the last 

 edition of ' Siluria,' the reader must understand that the chocolate- 

 coloured horizontal sandstone extends over a larger area under the 

 peak of Queenaig than is there represented. 



In regard to the base of the Cambrian or Longmynd sandstone, as 

 resting on the fundamental gneiss, it is well also to point the special 

 attention of travelling geologists to the junctions near the Gwalin 



