1869.] Mineralogy. 451 



In association with Mr. P. J. Butler — a gentleman possessing 

 a fine collection of gems — Mr. Sorby has presented to the Eoyal 

 Society a paper " On the the Structure of Kubies, Sapphires, Dia- 

 monds, and certain other Minerals."* They find that the sapphire 

 exhibits numerous cavities, sometimes reaching iVth of an inch in 

 diameter, and either partially or entirely filled with a liquid — pro- 

 bably condensed carbonic acid. Small triangular lamellar crystals 

 are also to be noted as common inclosures in this gem. The ruby 

 differs from the sapphire — although of com-se chemically the same 

 stone — in that it contains fewer fluid-cavities and more included 

 crystals, some of which are octohedral in form, and are probably 

 minute spinel rubies. In certain spinels from Ceylon, the fluid- 

 cavities contain a colomdess hquid, accompanied by either a sohd 

 substance or a very viscous fluid in which small crystals are em- 

 bedded. Many emeralds are extremely full of fluid-cavities, con- 

 taining what appears to be a strong saline solution with cubic 

 crystals — probably of chloride of potassium. By examining several 

 diamonds, the authors find that the embedded black specks, which 

 Brewster imagined might be cavities, are really inclosed crystals. 

 Some of these are surrounded by cracks indicating contraction in 

 the neighbouring mass ; and this indication is strengthened by the 

 appearance of a black cross surrounding the crystals when examined 

 by polarized Hght. The authors' general conclusions drawn from 

 these observations " seem to show that the ruby, sapphire, spinel, 

 and emerald were formed at a moderately high temperature, under 

 so great a pressm'e that water might be present in a liquid state. 

 The whole structure of the diamond is so peculiar that it can scarcely 

 be looked upon as positive evidence of a high temperature, though 

 not at all opposed to that supposition." 



When Mr. David Forbes, more than eighteen months ago, pub- 

 hshed the first part of his researches in British mineralogy, he 

 described at length the results of his examination of our Welsh 

 gold. Since then, his attention has been directed to the gold-bear- 

 ing districts of England, Ireland, and Scotland, as represented 

 respectively by the counties of Cornwall, Wicklow, and Sutherland.! 

 By examining specimens from each of these localities, Mr. Forbes is 

 enabled to place in our hands a series of analyses of gold from every 

 quarter of the British Isles — a series peculiarly valuable, inasmuch 

 as our knowledge of the chemical composition of British gold has 

 hitherto been remarkably defective. As we have already pubhshed 



* ' Proceedings of the Royal Society,' xvii., No. 109, p. 291. 

 t ' Philosophical Magazine,' May, 1869, p. 321. 



