182 



MINERALS AND GEOLOGY 



obscure. They consist essentially of Jabradorite or albite, or of 

 mixtures of these and other triclinic feldspars. Their colour is. 

 mostly white, light-grey, pale lavender-blue or greenish-white ; but 

 some are pale-red or yellowish ; and the cleavage planes occasionally 

 show the green or greenish-blue reflected tints characteristic of la- 

 bradorite. All become opaque-white by weathering. Bronze-coloured- 

 or dark -green hypersthene, in foliated examples, is sometimes present 

 in them, as at Chateau Richer and elsewhere. This variety has been 

 termed Hyperite or Hypersthene rock. 



3. Traps and Greenstones: The rocks of this series present a 

 somewhat variable composition, but consist essentially of some kind 

 of feldspar usually Labradorite or Albite or a mixture of feld- 

 spars, with augite, hornblende or chlorite. Many also contain in 

 addition, a mixture of zeolitic minerals, nepheline, magnetic and 

 titaniferous iron ores, grains of olivine, scales of mica, carbonates of 

 lime and iron, and other substances. But free silica or quartz is 

 altogether absent, or is present only as an accidental or inessential 

 constituent. The texture of these rocks is of two general or princi- 

 pal kinds : .(1), compact or homogeneous; and (2), distinctly granu- 

 lar or granitic ; but fine-grained examples offer a transition from th& 

 granitic to compact structure. In the latter, the component minerals 

 are blended into a common or uniform mass, chiefly, unless weathered,, 

 of a grey, green or black colour. In each of these varieties of texture,. 

 a poq.hyritic structure (see Fig. 97, above) may also be present 

 the imbedded crystals consisting of albite, oligoclase, augite, horn- 

 blende or some other mineral. The compact varieties also frequently 

 exhibit an amygdaloidal structure, Fig. 98, the rock being full of 

 oval or irregularly-shaped cavities, usually of small size, and com- 

 monly lined or filled with amethyst, agate,. 

 or other varieties of quartz, or otherwise 

 with calcspar, various zeolites, green- 

 earth, &c. These compact varieties, 

 moreover, ' of both trap and greenstone 

 very often assume a columnar or basalti- 

 form structure, as in figure 99. In this 

 case the rock exhibits a kind of rough 

 crystallization, and contains numerous 



FIG. 98. 



