﻿1861.] MTJUCHISON AND CfEIKIE STRATA OF THE HIGHLANDS. 235 



recognizes the existence of stratification-planes, and the parallelism 

 of these as a whole with the interlaminations of quartz *. 



The late Mr. Daniel Sharpe, in his memoir, endeavoured to prove 

 that the foliation-laminse of the gneiss were arranged in great arches, 

 ranging in a JST.E. and S.W. direction. But true slatj cleavage, as we 

 have already remarked in our preceding memoir, is rarely met with 

 in the Highlands, and where it does occur, it is nearly always 

 more or less transverse to the planes of stratification. Again, whilst 

 Mr. Sharpe does advert to rare examples of cleavage-planes tra- 

 versing those laminas which he refers to foliation (Phil. Trans. 1852, 

 vol. cxlii. p. 449, and pi. 23, figs. 1, 3, 4), he maintains throughout 

 his memoir, and illustrates the view in his general sections, that all 

 those bands of different mineral matter which we have shown in 

 preceding memoirs to be successive deposits, are due to foliation only. 

 He altogether loses sight of the great intercalations of limestone, some 

 of which, as we have formerly shown, contain organic remains. Let 

 us now give some illustrations of our views. 



At Dunkeld in Perthshire, at Easdale in Argyllshire, or at Bally - 

 hulish, where true cleavage exists, it is seen to cut through those 

 lines of colour, by which, in finely levigated clay-slates of a homo- 

 geneous composition, the original laminae of deposit are recognized. 

 In the argillaceous schists on the flanks of the Grampians, and 

 notably near the Spittal of Gflenshee, where the strata are often 

 violently contorted, as seen in the specimen we now exhibit f, the 

 cleavage-planes are rudely parallel to each other, and cut right 

 across the undulating layers of black carbonaceous schist. This 

 specimen is indeed a good example of the view now adopted, that 

 the parallel planes of cleavage are due to lateral pressure ; for here 

 we have a proof that the original beds of carbonaceous shale have 

 been so intensely squeezed up as to produce the contortions exhi- 

 bited, whilst the cleavage-planes traverse them. We have also at 

 hand in this locality the explanation of these contortions in the exist- 

 ence of numerous points or bosses of syenite, porphyry, and other 

 similar rocks, which protrude to the surface around the Spittal of 

 G-lenshee. The compressed schist to which we allude is so highly 

 carbonaceous in the little burn to the west of the inn at the Spittal, 



* Professor Ramsay, in a paper read before the Geological Society (Quart. 

 Journ. Geol. Soc. vol. ix. p. 172), discusses the metamorphism of Anglesea, and 

 refers it to a period anterior to that of the cleavage of the Welsh slates. He 

 adds, that " if the rocks be uncleared when metamorphism takes place, the folia- 

 tion-planes will be apt to coincide with those of bedding ; but if intense cleavage 

 has occurred, then we may expect that the planes of foliation will lie in the planes 

 of cleavage." And in the letter-press explanation of Sheet 40 of the Horizontal 

 Sections of the Geological Survey, he unhesitatingly declares his belief, that the 

 metamorphic rocks of Anglesea are the prolongation of the green and purple 

 grits and slaty rocks of Bangor ; and that, moreover, they are disposed along an 

 anticlinal axis, the S.E. side of which consists of the higher part of the Cambrian 

 series, overlaid by the Lower Silurian, while the N.W. side brings down the 

 same succession, though broken by a line of fault, " thus comjjleting the series, 

 and adding to the probability of the Cambrian age of most of the metamorphic 

 rocks of Anglesea." 



X This specimen is deposited in the Museum of Practical Geology. 



