166 HARRIS. MINERALS. 



finest sugar as well in the splendour of its colour as 

 the minuteness of its texture, but passes by degrees into 

 the compact form. 



Sahlite is the most interesting mineral found 

 in Harris, where it is scarcely less various in aspect 

 or less abundant than in Tirey. It has already been 

 observed that it occurs here in the limestone, as it 

 also does in Glen Elg, in Glen Tilt, and in Tirey ; either 

 .occupying distinct cavities, or else firmly imbedded 

 in the rock. It is sometimes crystallized in very flat- 

 tened rhombic prisms with curved sides and summits; 

 the latter being dihedral, and the crystals of an inch 

 in length. It is also found in irregular flattened hexaedral 

 or octaedral prisms, most generally imbedded in the 

 limestone. The colour is various, being either black, 

 white, grey, greenish, or brown, two or more of these 

 differently coloured concretions occasionally combining 

 in the same mass. In texture it is sometimes opake, 

 while in other cases it approaches to the vitreous aspect, 

 exhibiting at the same time all the intermediate modi- 

 fications. One variety is deserving of notice from its 

 resemblance to a mineral to which the name of bronzite 

 has been applied, and which, according to Hauy, belongs 

 to the species diallage. This is of a clear umber brown, 

 with somewhat of a metallic splendour, the structure being 

 lamellar and approaching to the fibrous. In other respects 

 it has the character of pyroxene, the angles of the in- 

 tegrant prism measuring 88 and 92 nearly ; whereas 

 those of diallage are almost equal, the more obtuse angle 

 not much exceeding 90. It is not unlikely that a 

 further investigation of the several minerals classed under 

 these different species may throw light on a subject at 

 present somewhat obscure, and lead to the more ac- 

 curate classification of some substances of which the 

 affinities are as yet uncertain. The other form of the 

 sahlite or pyroxene here occurring, is that of coccolite, 

 or a congeries of independent and ill-determined minute 



