".3<; 



In the calculation of the mode the assumption was made 

 that all the iron in the ferric state was in haematite, that 

 all the alumina was in the picotite, and that the ratio of 

 magnesia and ferrous oxide in the spinel was identical with 

 that in the picotite of the analysed dunite. The very 

 small amount of alumina effectively disproves the former 

 presence of anorthite in any considerable quantity, more 

 especially as the large amount of spinel and small per- 

 centage of chromium show how high must be the alumina 

 content of that mineral. As might be expected, a good 

 deal of lime has been brought in by the carbonating solu- 



A quartz-carbonate rock occurs which has been derived 

 from a harzburgite. It consists of enstatite and diallage, 

 both perfectly fresh, embedded in a mass of finely granular 

 quartz, separated into major grains by layers of dusty 

 carbonate. Picotite is present split by fissures which have 

 been filled by carbonate also. Small veins of basalt are 

 present containing minute flakes of biotite. 



These observations throw considerable doubt on the 

 determination 1 by previous workers of a chromite-anorthite 

 rock. The chromite is probably picotite, as shown by the 

 chemical analyses, though this distinction was not possible 

 by the methods used in the earlier determination. Its 

 occurrence makes the presence of felspar very improbable- 

 Moreover in their account of the microscopic features of 

 the felspar, they do not mention that it is twinned, or 

 biaxial, or even showing cleavage. They specially note its 

 resemblance in shape and cracking to the felspars of a 

 troctolite. Further they note the presence of the greenish 

 silicate, and also remark that in hydrochloric acid the 

 mineral effervesces briskly. Their specific gravity deter- 

 mination of the "anorthite" would also be given by an 



1 Proc. Roy. Soc. X.S.W., 1893, p. 403 et seq. 



