Tlie Trcqyrain Laiv Plionolite. 517 



a faint but irregular cleavage parallel to (010). Nearly all such crystals 

 extinguished parallel to the cleavages. 



From the above characteristics the mineral was suspected to be 

 olivine in spite of the unusual ophitic mode of occurrence. The 

 mineral occurred abundantly in the rock, but not so frequently as 

 the pleochroic augite. In a few slides it was absent. 



MiCROCHEMICAL AND ChEMICAL EXAMINATION.^ 



Nepheline.- — Li order to test the supposed nepheline, three slides 

 were subjected to the same microchemical staining process employed 

 by Dr. Hatch (4 and 5). Over twenty patches of the supposed 

 nepheline were noted and their positions recorded both by sketches 

 and by co-ordinates on the grid engraved on the fixed stage of a 

 Dick microscope. Each slide was then cleaned with benzol and 

 covered with a few drops of concentrated hydrochloric acid. Five 

 mmutes acid treatment was found to be quite sufficient. The slide 

 was then carefully washed for about twenty minutes ia a very gentle 

 stream of running water in a flat dish, treated with a solution of 

 fuchsrne, and again carefully washed. Every marked patch of 

 supposed nepheline was stained and stood out distinctly from the 

 unaffected felspars. It was found that staining was unnecessary, 

 as the gelatinized patches could be clearly seen after the acid treat- 

 ment and washing. An even cleaner test was made in the case of 

 two slides by more prolonged treatment with acid, when the nepheline 

 was entirely removed and a hole left with the shape of the original 

 nepheline patch. 



This test confirmed the presence of nepheline. 



Analcite and Sodalite. — Isotropic patches were observed to 

 stain in the slides primarily used to test for nepheline, and 

 some of the isotropic material was seen to be attacked by the 

 acid much less readily than the nepheline. In order to test 

 further the nature of the isotropic material, patches were marked 

 as in the case of the nepheline, and the slide vvas covered with 

 a few drops of pure dilute nitric acid and silver nitrate for about 

 twenty minutes, and then carefully washed and exposed to sunlight. 

 Under the microscope different patches of the marked isotropic 

 material were now seen to present quite distinct characters. Some 

 had been highly corroded and were crowded with small black 

 grains, especially at the edges, and in consequence at once stood out 

 and caught the eye. Others were much less corroded, but had 

 acquired a very striking system of small reticulated cracks, quite 

 independent of cleavage (when the latter could be made out). These 

 cracks were just visible with the 1 in. objective. The cracked 

 patches had no deposit of black grains. Further, with the naked 

 eye the surface of the slide could be seen to be covered in parts with 



^ As explained above, the chemical analysis of the rock by Mr. Ennos is 

 reserved for Part II, where it is accompanied by a discussion of mineral 

 proportions. 



