GEOLOGY. 319 



ON SOME PHENOMENA OF CRYSTALLIZATION. 



Sir David Brewster, at the last meeting of the British Association, 

 after stating that crystals of titanium within quartz had been long 

 known andattended to, drew attention to the fact that regular crys- 

 tals of tourmaline, titanium and quartz had been discovered by him 

 within mica, amethyst and topaz. That in some instances these crys- 

 tals had been found grouped in very regular figures, and that the 

 groups of crystals were sometimes distributed over what were obviously 

 surfaces of 'inner crystalline forms of exactly the same shape as the 

 entire crystal, from which the author drew inferences as to the orig- 

 inal growing of the crystal. 



CURIOUS EXAMPLE OF CRYSTALLIZATION. 



At the British Association, some curious crystals were exhibited by 

 Mr. J. Pearsoll, which were obtained while searching the coast of 

 Africa, between Saldanha Bay and the island of Ichaboe, for guano 

 deposits. The crystals are of carbonate of lime, inclosing sand ; 15 to 

 20 per cent, of sand is obtained from some specimens. The crystals 

 are very hard, and have sharp cutting edges, so as to make it a painful 

 task to walk upon them. The beach was covered with crystals to the 

 extent of miles ; and was from one-half to one mile in breadth. 

 Some of the specimens are from four to five inches in length, and with 

 surfaces showing a thickness of half an inch, and from two to three 

 inches across the plane. The report given was that some of the crys- 

 tals protruded up from the sands so far as to wound the. ankles and legs 

 without great care in walking over them. Some crystals seem to be 

 opaque, with the sand inclosed except at the edges. Carbonate of lime 

 and magnesia, with small quantities of saline matter, common salt princi- 

 pally, can be obtained by breaking them up in distilled water. They are 

 entirely soluble in diluted nitric acid. Mineralogists and chemists are 

 perfectly well aware of the stony substance called Fontainebleau sand- 

 stone, in which the sandstone is found having forms of crystals of 

 carbonate of lime. The crystals exhibited show the grains of sand 

 of the beach inclosed, without altering the general Ibrm, and also 

 that the crystal has, at its base, adapted itself to the sand and other 

 crystals. 



ARTIFICIAL FORMATION OF MINERALS BY IGNEOUS ACTION. 



Prof. Hausmann, of Gottingen, has recently published a memoir on 

 the formation of minerals in and about furnaces by furnace action. 

 He enumerates the Ibllowing varieties observed by him : Silver, lead, 

 copper, iron, bismuth, lead-glance, blende, oxide of zinc, red-copper 

 ore, iron-glance, magnetic iron ore, crysolite, pyroxene containing 

 alumina, Humboldtite, orthoclase, lead-vitriol, and arseniate of nickel. 

 Brown, yellow, green, and black blende were observed formed in the 



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