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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 20, 



Highlands of Scotland, or to any mountain-tracts in Europe which 

 ■we have explored. In fact, all our contemporaries, with whom or 

 with whose works we are acquainted, have treated such larninse 

 as marking, on the whole, the lines of original stratification. Thus, 

 in 1827, when one of us explored the Highlands with Professor 

 Sedgwick, that distinguished man clearly pointed out, in situ, the 

 absolute independence of such foliation and cleavage ; and thence- 

 forward, and after repeated surveys of the same region during suc- 

 cessive years, we have, on various occasions *, expressed our entire 

 dissent from the doctrine and opinions of the lamented Mr. Daniel 

 Sharpe, recorded in a memoir entitled " On the Arrangement of 

 the Foliation and Cleavage of the Eocks of the North of Scotlandf 

 As early indeed as the year 1835, and consequently eleven years 

 before Mr. Darwin wrote, and seventeen years before the publica- 

 tion of Mr. Sharpe, Professor Sedgwick, in his remarkable " Me- 

 moir on the Structure of large Mineral Masses," actually enunciated 

 the distinctions on which we insist in this memoir. In speaking 

 of those ciystalline schists of parts of England and Wales, and of 

 the Highlands of Scotland, which are " finely foliated," he goes on 

 to say : — " In general, however, the foliated uneven layers of these 

 older formations belong, I believe, to beds, and not to cleavage- 

 planes; and the oldest and most crystalline rocks, designated by 

 the general term of schists, have no true slaty cleavage in the sense 

 in which I have used the term +." 



Professor Sedgwick thus defines these distinctions : — " Bed is 

 always applied as the English synonym of stratum ; and the words 

 thick-bedded, thin-bedded, thick-flaggy, thin-flaggy, and laminated, 

 are words in common use, and express well enough different modi- 

 fications of stratified structure. The term foliated, again, expresses 

 very well the peculiar structure of mica-schist, and the fine, glossy, 

 undulating layers of greywacke." After enumerating the essential 

 difference between slaty and flaggy structure, he adds : — " In this 

 way, foliated as distinct from laminated, and slaty as distinct from 

 flaggy, become terms of a definite meaning §." 



It should be further remembered, that in the year 1840, and also 

 before Mr. Darwin's observations were published, the Local Di- 

 rector of the Geological Survey, Professor Ramsay, devoted himself 

 specially to a careful survey of Arran, and in the early part of the 

 following year published a descriptive account of the geology of 

 that island. In speculating upon the origin of the quartz -layers 

 that are interbedded in its schists, he remarks that these quartz- 

 layers " he in regular lamina?, very numerous, and parallel to the 

 plane of stratification. Sometimes these alternations are almost 

 as minute as the leaves of a closed volume." He thus clearly 



* Report Brit. Assoc. Glasgow, 1855, Trans, of Sections, p. 86. Siluria, 2nd 

 edit. pp. 179. 195. Quart. Journ. Greol. Soc. vol. vii. p. 168 ; and vol. xv. p. 391. 



t See Philosophical Transactions, vol. cxlii. p. 445 (1852) ; with a coloured 

 map of Scotland and sections. 



I Trans. Geol. Soc, new series, vol. iii. p. 479. 



§ Ibid. p. 480. 



