190 THE GEOLOGY OF THE CANOBOLAS MOUNTAIN'S, 



structure. They are twinned on the Carlsbad and Albite laws, 

 and have the properties of andesine. Allotriomorphic ortboclase, 

 with shadowy extinction, seems also to be present in minute 

 amount. The augite, in hypidiomorphic crystals, is a brownish, 

 titaniferous variety, with extinction angle 45*^'. Colourless 

 olivine occurs also in hypidiomorphic grains. A little red 

 fayalite, ragged plates of ilmenite, and idiomorphic magnetite 

 grains (titaniferous) are all present. Chlorite and red iron-ores 

 occur as decomposition-products. In addition, we have some 

 isotropic, or nearly isotropic, colourless to yellowish-green 

 minerals lying interstitially. The chief of these has a character- 

 istic peg-structure, indicating that it is melilite. The pegs con- 

 sist of apatite, and magnetite grains are also abundantly included. 

 As the pegs in melilite lie perpendicular to the basal plane, it is 

 found that the mineral under discussion, if it be melilite, has 

 a perpendicular to the C crj^stallographic axis, and is optically 

 negative (Bx = a). The R.I. is medium, and its D.R. very low. 

 Shape always allotriomorphic. 



Another totally isotropic, colourless constituent, probably 

 analcite, is also present. 



Order of Consolidation. 



1. [Imeaite 



2. Olivine 



3. Augite 



4. Felspar 



5. ?>Iagnetite 



6. Apatite 



7. Melilite(?) ■ 



8. Glass (analcite V) 



Kame : Ophitic Olivine-Melilite Basalt. 



Note. — The rocks indicated by the letter X., followed by a 

 reference number, belong to the Technical College Collection 

 gathered together by Mr. Siissmilch on several visits. Those 

 indicated by the letter C, belong to my own collection (H.I.J.). 



