WRITINGS OF JAMES SMITHSON. 71 



has no acquaintance ; which he never has beheld in action ; 

 to whose indisputable results he is an utter stranger j who 

 engages in the fabrication of a world alike unskilled in the 

 forces and the materials which he employs. 



AN ACCOUNT OF A NATIVE COMBINATION OF 

 SULPHATE OF BARIUM AND FLUORIDE OF 

 CALCIUM. 



From Thomson's Annals of Philosophy, Vol. XVI, 1820, p. 48. 



Paris, March 24, 1820. 



Sir : I acquired this substance in Derbyshire. It is many 

 years since I ascertained its constitution. I have examined 

 several minerals which in appearance bore a resemblance to 

 it, but have not found any of them to be of the same nature. 

 This species would hence appear to be of rare occurrence 

 in the earth. 



This substance formed a vein about an inch wide in a 

 coarse shell limestone. Next to this substance was a layer 

 of crystals of sulphuret of lead ; and between these and 

 the limestone rock a layer of crystals of carbonate of cal- 

 cium. 



I infer that these matters filled a vertical fissure in the 

 limestone stratum ; and from -the ideas I entertain of the 

 mode by which such fissures have generally become occu- 

 pied by their contents, I believe them to have been succes- 

 sively deposited in it by sublimation, either through the 

 intense vehemence of subterranean fire, or by the agency of 

 the vapour of water, or of some other gas. 



This compound matter bears in its general appearance so 

 strong a resemblance to fine compact grey limestone that 

 the eye can probably not distinguish bet^veen them. 



Forty-two grains of it lost 11.2 grs. in rain water at the 



