24-6 Sir David Brewster on the Structure 



air within both substances, the expansive force of which has 

 communicated a polarizing structure to the parts in immediate 

 contact with the air. This structure is displayed in four sec- 

 tors of polarized light encircling the globule of air, and can 

 be produced artificially either in glass or in gelatinous masses 

 by a compressing force propagated circularly from a point. It 

 is obvious that such an effect cannot arise from any mode of 

 crystallization ; and if any proof of this were necessary, it 

 might be sufficient to state that I have never observed the 

 slightest trace of it in more than 200 mineral substances which 

 I have examined, nor in any of the artificial salts from aqueous 

 solutions. It can, therefore, arise only from the expansive 

 force exerted by the included air in the diamond and the am- 

 ber, when they were in such a soft state as to be susceptible 

 of compression from so small a force. That this compressible 

 state of the diamond could not arise from the action of heat 

 is manifest from the nature and recent formation of the soil in 

 which it is found; that it could not exist in a mass formed by 

 aqueous deposition is still more obvious; and hence we are 

 led to the conclusion rendered probable by other analogies, 

 that the diamond originates, like amber, from the consolida- 

 tion of, perhaps, vegetable matter, which gradually acquires a 

 crystalline form by the influence of time, and the slow action 

 of corpuscular forces. 



" As the preceding results were obtained from flat dia- 

 monds, which did not seem to have been regularly crystallized, 

 I was anxious to detect the same structure in those which 

 had a regular crystalline form. With this view I examined 

 several of the diamonds in Mr. Allan's collection, and was 

 fortunate enough not only to detect in a perfect octohedrai 

 crystal the same structure which I had observed in the flat 

 specimens, but also an air-bubble of considerable size, which 

 had produced by its expansion the polarizing structure al- 

 ready described." 



Since these observations were written, Dr. Voysey has 

 shown that the matrix of the diamonds produced in Southern 

 India is the sandstone breccia of the clayslate formation ; and 

 Captain Franklin has found that in Bundel Kund the rocky 

 matrix of the diamond is situated in sandstone which he ima- 

 gines to be the same as the new red sandstone of England, 

 that there is at least 400 feet of that rock below the lowest 

 diamond beds, and that there are strong indications of coal 

 underlying the whole mass. The following are Captain 

 Franklin's observations on the origin of this mineral: 



" There is another circumstance to which I must advert, 

 but I do so with diffidence, and under a hope that it will be 



