8 GEOLOGICAL MEMOIES. 



of fluorine with other elements ; fluor spar, its production, association, 

 and pseudomorphic forms, and the more complex minerals cryolite, 

 topaz, and pycnite. It is suggested that the latter may be formed 

 from cryolite, a double fluoride of sodium and aluminium, when the 

 fluoride of sodium is replaced by a silicate of alumina, topaz being pro- 

 duced when the same replacement afl"ects a portion of the fluoride of 

 aluminium. 



In chapter xx. the alkaline and earthy carbonates are treated at 

 considerable length, commencing with the degree of solubility of 

 artificial and natural carbonates of lime ; then follow the methods by 

 which calcareous pseudomorphs are formed. The carbonates of mag- 

 nesia, baryta, strontia, iron, and manganese are treated in a similar 

 manner, but the interesting subject of the formation of dolomite is 

 reserved for the next volume. The subject of the composition of the 

 natural carbonates of iron, sparry iron ore, clay -ironstone, black band, 

 &c., is most elaborately treated, no less than fifty-seven analyses of 

 these minerals being given. 



Chapter xxi. treats of the difl'erent earthy sulphates, gypsum, 

 Epsomite, heavy spar, and celestine, their various methods of occur- 

 rence, transformations, &c. The difficulty of finding an origin for the 

 great masses of sulphate of baryta common in the newer mineral 

 deposits, no baryta-salt being recognizable in the composition of 

 crystalline rocks, is adverted to, as are also the recent researches of 

 Max Mitscherlich*, who announces the presenceof baryta, varying in 

 quantity from 0-45 to 2-33 per cent., in felspars from the Eifel and 

 S. Gothard. The production of sulphate of baryta by the double 

 decomposition of solutions containing witherite and gypsum is de- 

 scribed at length, with numerical illustrations. 



Chapter xxii. on phosphates, commences with a notice of the various 

 minerals containing phosphoric acid other than the ores of the heavy 

 metals ; the author then treats of Eownes's investigations on the 

 presence of phosphates in crystalline rocks and lavas, and proceeds 

 to consider the solubility of the difl'erent substances containing phos- 

 phate of lime in water saturated with carbonic acid. This varies very 

 greatly, apatite requiring 393,000 parts of water for complete solu- 

 tion, while the scrapings of the bones of a freshly killed ox dissolve 

 in 4000 parts, and precipitated neutral phosphate of lime requires only 

 1500 parts. Phosphate of lime is formed when alkaline phosphates 

 are heated with silicate of lime. "When phosphate of lime dissolved 

 in carbonated water is brought into contact with alkaline fluorides, 

 fluoride of calcium is deposited and phosphate of soda remains in 

 solution. This reaction is suggested as a probable cause of the increase 

 of fluorine in fossil bones. Phosphate of iron (Yivianite) is noticed 

 at some length, and a description is given of its occurrence in the 

 bones forming the skeleton of a drowned miner, which was found 

 in the Scharley zinc-mine in Silesia, upon reopening the workings 

 after they had been closed for three centuries. Yivianite may be 

 produced by double decomposition from apatite and sulphate or car- 

 bonate of iron. Notices of the best known occurrences of phosphates 



* Pogg. Ann. vol. cxi. p. 351. 



