93 



crystalline calcite of the vesicles, showing characteristic twin 

 structure and intersecting cleavage lines, appears to have 

 crystallised out synchronously with the delessite, judging 

 from its optical continuity notwithstanding interruptions by 

 delessite. 



Grains of iron ore, probably the carbonate, white in re- 

 flected light, are plentifully scattered through the base, and 

 often tend to collect round the outlines of the cavities. 

 There is an admixture of iron oxide, and some quadrate 

 forms are presented by small cubes of pyrites, distinguish- 

 able by their brassy lustre. The granular substance of the 

 siderite is discernible with a high power (|") . 



I can find no augite, and the chloritoid mineral is not 

 pseudomorphic after augite, but that mineral cannot have 

 been far off. We thus see that this reck has as its essential 

 constituents : — Glass with crystallites in the form of globu- 

 lites ; felspar crystals of the base, labradorite ; iron oxide, 

 probably magnetite. And as secondary and accessory con- 

 stituents : — Crystalline calcite occupying vesicles and veins ; 

 delessite in the vesicles ; quartz in vesicles ; carbonate of 

 iron in the base and also in the vesicles. This is evidently 

 an alteration product from the oxide. 



From the triclinic nature of the felspar and the sj^ecific 

 gravity (2 8) we infer that the rock belongs to the basic 

 division. Its light colour seems to be due chiefly to the 

 calcite and carbonate of iron, and masks its basic relations. 



We are thus led to include it among the glassy melaphyres. 

 Melaphyre is regarded by English petrologists as altered 

 basalt, and in this sense the Zeehan stone is the vesicular 

 form of old basaltic eruj^tive material = altered vesicular basalt 

 = vesicular melaphyre. Its microscopical characters there- 

 fore teach us that it is an old lava, and Mr. W. F. Petterd 

 says that in one of the adits of the Oonah Mine it can be 

 distinctly seen lying between the silurian slates and following 

 their stratification. Its European equivalent is the vesicular 

 spilite of Nassau, the so-called lime diabase. 



Since the preparation of this paper, Mr. Petterd has had 

 some slices cut from the more solid rock met with at a 

 greater depth, viz., from the 120ft. level of No. 3 shaft in the 

 Silver Queen Mine. These show only a few vesicles, but 

 have pale green chloritic materal diffused abundantly through 

 the base. The felspars are larger than in the surface variety, 

 but the same curved and distorted forms prevail. There is 

 carbonate ©f iron scattered over the field in grains, as well as 

 what I take to be titaniferous iron bordered by its white 

 alteration product leucoxene, sometimes in wedge-shaped 

 crystals, or pseudomorphic after felspar (and apatite ?) and 

 apparently so after olivine. The latter is the nearest ap- 

 proach which I can find to any porphyritic constituent. 



