70 On 1 [NES Of I [ELD-GEOD 



Red. The prevailing hue of red i MM .1 



brownish -red to a bright brick -red, and is due to the 

 presence of the anhydrous peroxide of iron (ferric oxide, 

 haematite). Such rocks are often mottled with or pass 

 into yellow and brown tints, where the iron they contain 

 has been hydr.iud. These colours are most typically 

 displayed among red sandstones and clays, of which an 

 enormous mass occurs in the Old Red and New Red 

 Sandstone, and in the Permian series. Some rocks show 

 a delicate flesh-red tint from the colour of their orthoclase 

 felspar, as in pink granite. Iron is in this case also the 

 pigment. 



Green. Many red sandstones are marked with circular 

 spots of green, due to the reduction of the iron -oxide. 

 Protosilicate of iron is the prevalent green pigment of 

 rocks ; carbonates of copper sometimes colour rocks of 

 bright verdigris and emerald -green tints. Many mag- 

 i.rMun silicates are green, and impart green colours of 

 various hues to the rocks of which they are constituents. 

 Thus hornblende and augite give rise to dark bottle- 

 green, and among the schistose rocks to paler apple-green 

 and leek-green tints. Epidote diffused abundantly 

 through a rock gives it a yellowish or grass-green hue. 

 The hydrous magnesian silicates, talc, chlorite, and ser- 

 pentine, form characteristically green rocks, the talc rocks 

 shading off through leek-green or apple-green into white, 

 and serpentine into black and dark red. Glauconite 

 extensively diffused through certain sandstones gives 

 them a characteristic green colour, as in the well-known 

 Green Sand. 



Blue is not a frequent colour in rock masses. It is 



