G E A 



[204] 



GEE 



orthocera, of which certain species 

 are also found in the carboniferous 

 limestone, but in no deposit more 

 recent. Some of the shells belong 

 to more recent genera, as the tere- 

 bratula. The only vertebrated re- 

 mains hitherto found are a few 

 bones of fishes. 



The most abundant shells of the 

 grauwacke belong to Orthoceras, 

 Producta, Spirifer, and Terebratula. 

 Some orthoceratites are found of 

 large size, of a yard or more in 

 length. Productse are common in 

 the grauwacke as well as in the 

 carboniferous group, they are also 

 found in the zechstein or magnesian 

 limestone, above which they dis- 

 appear. Spirifers are found as high 

 up as the lias, and consequently 

 continued to exist to a later period 

 than Products. Terebratulae, how- 

 ever, have survived all the great 

 changes which have occurred, and 

 are to be found amongst existing 

 genera. 



Graywacke abounds in Germany 

 and in Scotland; indeed, nearly all 

 the mountains of Scotland north of 

 the Frith of Forth are chiefly com- 

 posed of it. In the neighbourhood 

 of Mont Blanc, and in other parts 

 of the Alps, it oocurs at a great 

 elevation, forming large masses in 

 vertical beds. 



GBA'YWACKE SLATE. A variety of 

 graywacke, in which the grains are 

 so minute as to be scarcely per- 

 ceptible by the naked eye. 



GEEEN-EAKTH. The Griin Erde of 

 Werner; the Talc Zographique of 

 Haiiy; the Chlorite Baldogee of 

 Brongniart. A variety of talc, 

 occurring in vesicular cavities in 

 amygdaloid. Its colour is a plea- 

 sant green, more or less deep, 

 sometimes bluish or grayish-green, 

 and passing to olive and blackish- 

 green. Its fracture is dull, and 

 fine-grained earthy, or slighty eon- 

 choidal. It is somewhat unctuous 

 to the touch, and adheres to the 



tongue. Easily reducible to powder. 

 Specific gravity 2 '63. Kirwan. 



According to Yauquelin it consists 

 of silex 52, magnesia 6, oxide of 

 iron 23 '4, alumina 7, potash 7 '4, 

 water 4. It is met with in the 

 mountainous districts of England 

 and Scotland. It is the mountain- 

 green of artists ; and, when ground 

 with oil, is employed as a paint. 

 GBEEN-SAND. (glauconie sdbletise, Fr. 

 grunsand, Germ.) A member of 

 the chalk formation, called also 

 Shanklin sand. The beds of sand, 

 sandstone, and limestone, which 

 form the lowermost strata of the 

 chalk formation, have obtained the 

 name of green-sand, from the cir- 

 cumstance of their containing a 

 considerable quantity of chlorite, or 

 green earth, scattered throughout 

 their substance. "The colouring 

 matter," says Dr. Turner, " of 

 green-sand sometimes appears in 

 the rock of its ordinary green tint, 

 and sometimes in grains of so deep 

 a green that they seem black. The 

 former generally occurs in sand, or 

 where the sandstone is porous, and 

 in this state an ochreous appearance 

 is often observed, due to the green 

 particles being partially decomposed 

 and their iron having passed into a 

 higher state of oxidation ; whereas 

 the black looking grains are met 

 with in a highly calcareous sand- 

 stone, where the texture is too firm 

 to admit of the percolation of water. 

 From either kind of rock the green 

 matter may be obtained by washing 

 with water and subsidence, since 

 the colouring matter subsides less 

 readily than grains of quartz, and 

 more readily than calcareous and 

 argillaceous substances. On re- 

 ducing the samples obtained to 

 powder, washing away the finer 

 particles with pure water, and 

 separating any adhering carbonates 

 by dilute muriatic acid, the colour- 

 ing matter is left, mixed only with 

 small grains of quartz. It then 



