Geological Society. 2 1 9 



In the concluding section the author offers various suggestions re- 

 specting the most eligible mode of making observations on the tides, 

 and of correctly reducing them when made. 



GEOLOGICAL SOCIETY. 



February 27.' — A paper, commenced during the last Session, en- 

 titled "Description of Parts of the Kingdoms of Valencia, Murcia, 

 and Granada, in the South of Spain," by Capt. Cook, R.N. F.G.S., 

 was concluded. 



A paper entitled "Observations relative to the Structure and 

 Origin of the Diamond," by Sir David Brewster, K.C.H. LL.D. 

 F.G.S. &c, was then read. 



In the year 1820, the author communicated to the Royal Society 

 of Edinburgh a singular fact relative to the structure of the dia- 

 mond, accompanied with some conjectures respecting the origin of 

 this remarkable gem : — the present essay may be viewed as a con- 

 tinuation and extension of the same inquiry. 



The author refers to the remark of Newton, that amber and the 

 diamond have a refractive power three times greater in respect of 

 their densities than several other substances ; and he quotes New- 

 ton's conjecture, founded on that remark, of the diamond being 

 probably, like amber, an unctuous substance coagulated. In proof 

 of the intimate relation between the inflammability and absolute 

 refractive power of bodies, Sir D. Brewster adds the facts, that 

 sulphur and phosphorus exceed even the diamond in absolute power 

 of refraction, and that these three inflammables stand before all 

 solid and fluid substances in their absolute action upon light. 



Another close analogy between the diamond and amber, inde- 

 pendently of their like locality and carbonaceous nature, was traced 

 by the author in their polarizing structure. Both of these minerals 

 contain within their substance small cells or cavities, filled with air, 

 the expansive force of which has communicated a polarizing struc- 

 ture to the parts in immediate contact with the air. The descrip- 

 tion of this structure, which is displayed from sectors of polarized 

 light encircling the globule of air, is illustrated by drawings. 



The author contends that the peculiar polarizing power around 

 the cavities in amber and in the diamond must have been occa- 

 sioned by the expansive force of the confined substance, supposed 

 to be gaseous, compressing the sides of the cells, while the sub- 

 stance of the minerals was in a soft and yielding condition. A 

 similar structure may be produced in glass, or in gelatinous masses, 

 by a compressing force, propagated circularly from a point. 



Having thus shown that the diamond was at one time in a soft or 

 pasty state, the author argues that this state was not produced by 

 igneous fusion. For in his laborious examination of the cavities in 

 crystals, both natural and artificial, such as topaz, quartz, amethyst, 

 chrysoberyl, &c, and in salts, he observed the condition of many 

 thousand cavities ; but in no case, neither in crystals formed by 

 means of igneous fusion nor by aqueous solution, did he observe 



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