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GEOLOGICAL MEMOIRS. 



hyacinth-red, and which when finely pounded yielded a citron-yellow 

 powder. I found its specific gravity at a temperature of distilled 

 water of 15° R. hy one experiment to be 2*762, and by a second 

 2*761, while the specific gravity of native foliated Rauschgelb accord- 

 ing to Karsten is 3*459. The hardness is that of calc-spar, 3*, 

 while that of the foliated Rauschgelb is 1*5. Thus orpiment ap- 

 pears not only by its elementary proportions to be related to arsenious 

 acid, but also is analogous to it in being able to assume the crystal- 

 line as well as the amorphous state ; and that in this latter state it 

 is less dense but harder than in the crystalline. Orpiment seems 

 never to occur in nature in any but the crystalline state. 



Arsenious acid takes up sulphuret of arsenic, whether amorphous 

 or crystalline, in indefinite proportions, and thereby acquires different 

 shades of red or yellow. This compound, which is to be looked on 

 as a mere mixture, can be seen in the crystals of arsenious acid, which 

 are produced by roasting arsenical ores ; as I have remarked at the 

 Ockerhiitte in the Lower Harz, and at the silver furnaces of St. An- 

 dreasberg. The arsenikglas produced at Reichenstein in Silesia, is 

 always made impure by some sulphuret of arsenic, in consequence of 

 magnetic or iron pyrites being mixed with arsenical pyrites in that lo- 

 cality ; and consequently it is always more or less coloured yellow. 

 However, it passes in the trade for the white glass, and in fact be- 

 comes white as it loses its transparency, as II err Seidensticker has 

 observed. A yellow arsenikglas is made purposely for commerce* 

 by subliming powdered arsenic with a little sulphur. The mineral, 

 described by mef under the name of powdery sulphuret of arsenic 

 (schlackiger Rauschgelb), which occurs in the upper parts of the Ka- 

 tharina Neufang mine at St. Andreasberg, as a secondary production, 

 has by later observations been proved to be a similar combination of 

 arsenious acid with arsenical pyrites, and must therefore in future be 

 placed with arsenikglas. I have since met with a similar product 

 formed from roasting the ores at the St. Andreasberg silver-mines. 



[J. C. M.] 



The Quadersandstein- or Chalk-Formation of Germany 

 (Das Quadei sandsteingebirge oder Kreidegebirge in Deutschland) . 

 By Hanns Bruno Geinitz. Freiberg, 1849-1850. 8vo, 

 pp. 292, with 12 lithographic plates. 



The first of the two sections into which this work is divided treats 

 of the stratigraphical conditions of the Cretaceous or Quadersandstein- 

 formation in Germany. On account of the absence of the true Chalk 

 throughout Germany, — or its presence only as a subordinate mem- 

 ber of the group of marly and calcareous rocks, separating the Upper 

 and the Lower Quadersandstein, — the author considers that the term 

 Chalk-formation [Kreidegebirge] should, as far as Germany is con- 

 cerned, wholly give place to that of Free-stone-formation [Quader- 

 sandsteingebirge, or rather Quadergebirge (p. 281)]. This is de- 

 scribed as comprising in general all the series of arenaceous, marly, 



* Karsten's Syst. of Metallurgy, iv. s. 574. 



f Nordd. Beitrage zur Berg imd Hiittenkunde, iv. s. 84. 



