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Published online by Cambridge University Press: 14 March 2018
The clays appear under many widely different aspects, and from one point of view must be studied as rocks. There are rock-masses alike of clay and of serpentine, both the result of important metamorphic processes. The basis, however, of most—probably of all—clays appears to be a substance of definite composition and well-marked characters, as much entitled to specific mineral rank as allophane or serpentine, or perhaps opal. In this paper I propose to consider clay as a rock and as a mineral.
page 205 note 1 J. H. Collins, F.G.S., 1878. The Hensbarrow Granite District.
page 205 note 2 Hensbarrow Granite, p. 31. This substance is ground up with clay and other ingredients in the manufacture of porcelain.
page 206 note 1 Professor Sedgwick (Camb. Phil. Trans. I. pp. 104-5) says—speaking of decomposed granite-rock in general—” on a near examination it is frequently found soft enough to be cat with a spade—and it is in that state packed up and exported to the potteries.” As a matter of fact China-Xone, which is exported to the potteries in its raw - state, is never soft enough to be cut with a spade; while China-clay, which may be so cut, is never so exported.
page 206 note 2 Sorby: Anniversary Address to Roy. Micros. Soc. 1877.
page 207 note 1 This is true of nearly all the analyses given by Prof. Macadam in No. 33 of the Min. Mag. p. 76. and notably of Nos. 1 to 7, 10 to 15, and 20 to 27. Boase's analysis of kaolin, quoted by Mr. Butler at p. 79 of the same No., was evidently made on faulty material, as is shown by the enormous quantity of alkali.
page 207 note 2 Address to the Boyal Microscopical Society, 1877.
page 207 note 3 Ibid. 127.
page 209 note 1 See S. W. Johnson and J. M. Blake. Am. Journ. Science, 2nd series. Vol. 43, p. 351.
page 212 note 1 Annales des Mine', XX. 1841. He used perchloride of tin, as being more readily obtained than the corresponding fluoride; but be argues, and few chemists will dispute it, that similar results would follow from the use1 of the fluoride. Tha use of the chloride instead of the fluoride may explain why the artificial oxide differed in form from the natural.
page 212 note 2 Min. Tasch. 1824.
page 212 note 3 Ann. des Mines, 1841.
page 212 note 4 See, for fuller details, my paper on “ Cornish Tinstones and Tin Capels,” Min. Mag. IV. pp. 123, 124, 1882.
page 213 note 1 Communicated to the Royal Institution of Cornwall some years since.
