CN GLAUCOPHANE. 91 



measurement, as it is impossible to find a good orientated section. 



Paramorphosis of the diallage is abrupt, and usually begins from 

 peripheries or from transversal fissures. The glaucophane is a small 

 columnar or very fine fibrous; in the latter case it may, perhaps, be 

 proper to call it crocidoUte, although it is not capable of a rigid proof, 

 on account of the minuteness of its size. The direction of fibres coin- 

 cides, as a rule, with that of the general mass of the rock without 

 regard to the position of diallage. The compact glaucophane again 

 resolves at its terminations into a fibrous crocidolitic mass which, 

 then, becomes grass-green in colour, and insensibly merges in the 

 general rock-mass. The colour of glaucophane and its derivative — 

 crocidolite, is deep green when the longest side is parallel to the short 

 diagonal of the lower nicol; at right angles to it, it is lavender-blue. 



The glaucophanized portion and the intact diallage are orientated 

 in the same direction, and extinguish the light in the direction of C\ 

 when view^ed from the orthopinacoid. On the clinopinacoid, however, 

 the extinctions do not occur simultaneously, but show great deviations; 

 and as the glaucophane-prisms are usually minute in size and the ex- 

 tinction-angles are so small, it appears as if were in the direction of the 



axis C. 



II. Amphibolite. 



Amphibolites form a member in the archœan complex ; their 

 external appearances are various, on one side they approach to an ash- 

 grey clay slate; on the other to a compact chlorite-schist ; thirdly they 

 have a close resemblance to an ordinary serpentine. So multifarious 

 are their outward aspects that the writer has been struck with the 

 simplicity of the mineralogical composition, when viewed under the 

 microscope. 



The microscope reveals to us no other ingredients than diallage 

 and its derivatives-glaucaphane, and a hardly definable chloritic 



