46 Scientific Proceedings, Royal Dublin Society. 



closed vessel at 180° 0. in presence of water, or in a saturated 

 solution of chloride of magnesium or chloride of calcium. The • 

 product obtained was red, amorphous, and resembling the common 

 variety of natural sesquioxyde of iron. Why the central band of 

 the crystal should alone present this oxyde is not so easily ex- 

 plained, unless by the hypothesis that crystals of either carbonate 

 of iron or iron pyrites were deposited on this surface, and then 

 subsequently transformed into peroxyde. That certain faces of 

 crystals induce, or facilitate such deposits is well known ; and that 

 the state of the surface of the face is an essential factor in the 

 phenomenon is also well known : the primary cause is, however, 

 less clearly explainable. 



That no precise conclusions could be drawn from the' presence 

 either of aragonite or calcspar as regards the temperature of the 

 solution from which the crystals were deposited would appear 

 from the synthetical experiments of Gr. Rose, which tend to prove 

 that both calcite and aragonite may be formed in warm solutions. 

 The conclusions of a review of all the synthetical experiments 

 made up to the present relative to these two minerals are thus stated 

 by Messieurs Fouqu^ and Levy in their remarkable work, " Syn- 

 these des mineraux et des roches " (1882), p. 203 : — " In the 

 greater number of cases, natural calcite and aragonite appear to 

 result from the decomposition of solutions of bicarbonate of lime 

 more or less concentrated, and more or less warm. The crystals 

 formed affect the rhombohedral, or rhombic forms according to the 

 temperature at which the crystallization takes place." 



In this case the presence of the red band of sesquioxyde of iron 

 would tend to prove that the solution, at one particular stage, was 

 warm, and as this was a final stage, the probability is that the 

 calcite crystals were formed from warm solutions of bicarbonate of 

 lime. 



