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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 20 t 



that some of the points of rock blacken paper like a black-lead, 

 pencil, and we therefore supposed it might be graphite ; but a che- 

 mical examination of it at the Government School of Mines by Mr. 

 C. Tookey has shown that it is simply highly carbonaceous black 

 schist, Avith some mica, the rock yielding on combustion nearly 16 

 per cent, of carbon. 



In arriving at the belief which we entertain, that all the " foli- 

 ation" of the crystalline rocks of the Highlands which we have 

 examined is nothing more than the original laminpe of deposit under 

 water, of sand, clay, lime, mica, &c, which have been so altered as 

 often to segregate in one layer more mica, and more sand or clay 

 in the others, thus evolving felspathic, quartzose, and micaceous 

 crystalline laminae, we are sustained in our inference by an appeal 

 to the whole succession of the mineral deposits of the north of 

 Scotland. For we have shown that these successive deposits are so 

 knit together by transition and conformable superposition, that it is 

 quite impossible to exclude from the series those of its members 

 which still exhibit not only a mechanical origin, but also contain 

 organic remains. From our old acquaintance with the late Mr. D. 

 Sharpe, we are convinced, that if, instead of making one rapid survey 

 only, in whicb, full of a new theory, he naturally applied it, with 

 his well-known energy, he had year after year examined these 

 Highland rocks, he would have seen the impossibility of excluding 

 (as he did) the greater part of the quartz-rock of Scotland from 

 the crystalline series, merely, as he says, because it is " an altered 

 sandstone of which the mineral character has been changed by plu- 

 tonic action." He would, we doubt not, on a more careful survey, 

 have seen that this very rock and its associated limestones are in- 

 tegral and even lower parts of a large portion of that same crystalline 

 sei'ies ; and then he would have admitted, that, as these pure quartz- 

 rocks (evidently nothing but altered sandstones, and in which Anne- 

 lides and an Orthoccratite have been found) graduate into micaceous 

 quartz-rocks, mica-schists, and gneissose rocks, they could not be 

 divided geologically into two separate classes, but form truly one 

 great series, varying in its mineralogical characters as well as in the 

 extent and form of its metarnorphism. 



The views which we entertain have been indeed, to a great extent, 

 sanctioned by the examination of the older rocks of the Highland 

 border by a very close and accurate observer of structure. Di- 

 stinctly objecting to the general application of the term foliation, Mr. 

 Sorby has shown that one of the structures of metamorpbie rocks 

 " has every character that would be the result of stratification, even 

 in some cases including the current structures *." 



Again, the same author, in his notice of the microscopical nature 

 of mica-schist, has demonstrated, that in one class of these rocks the 

 flakes of mica lie in the plane of the alternating layers of different 

 mineral composition, whilst in the other class the flakes of mica 

 traverse the original Hues of bedding like slaty cleavage. He there- 

 fore proposes the tonus " stratification-foliation " and " cleavage - 

 * Kepprt Brit. Assoc. Adv. of Science, 1855, Trans, of Sections, p. 96. 



