I.I II KM IN ATMX OF R0< 71 



oiun j.k. :. .'i . t . the olour of many limestone*, * 

 however, arc grey or bluish -grey. Beautiful belts of 

 pale blue and white occur among the schistose rocks 

 where the mineral kyanite abounds. Some days and 

 lnh .marges are of a pale L lue. Patches of a 



bright smalt t>! an indigo tint, may be met with 



: i -c.n mosses, where some animal organism has 

 decayed and given rise to the formation of phosphate of 

 . unite). 



fy may be said to be th ng colour among 



rocks, especially of the older geological period 



c rocks like limestones it is often produced by the 

 intermingling of minute panicles of clay, sand, or iron- 

 * '( amorphous carbonate of lime with the paler 

 crystalline calcite of the comminuted organisms. I'urc 

 crystalline limestone is naturally snow-white, as in Carrara 

 marble. In compound rocks the prevailing grey hues 

 depend on the- mixture oi a white mineral, usually a fel- 

 spar, with one or more dark minerals like magi 

 hornblende, or augite, the lightness or darkness of the 

 hue depending upon the relative proportions of the con- 

 stituents. Should the felspar be coloured 1> 

 pinkish hue may be given to the grey ; or if the dark 

 magnesian silicates have been altered into some of their 

 hydrous representatives, the grey becomes more or less 

 distinctly xreen. The old "greenstones" probably ori- 

 ginally grey, often owe their present <: hue to an 

 alteration of their original minerals, and especially to the 

 development of chlorite or :i them 



5. Smell- Its may be recognised by the 



peculiar earthy (argillaceous) odour they give out when 



