440 Transactions. — Geology. 



1865, pp. 264-436), but we have no specimen in the Museum. Professor 

 Liversidge again mentions the occurrence of this mineral at Dunedin 

 (Trans. N.Z. Inst., vol. x., p. 494), as well as a magnesian ironstone from 

 the Clutha. 



Splmrosiderite occurs as an accessory mineral in many of our volcanic 

 and dyke rocks. Thus Dr. Hector mentions it as occurring in basalt 

 (Jurors' Eep. N.Z. Ex., pp. 264 and 436), and Dr. Haast mentions its 

 occurrence in dyke rocks, and in the volcanic rocks of Banks Peninsula 

 and the melaphyres of Mount Somers (Jurors' Eep., p. 258 ; Geol. Eep., 

 1878-74, p. 4, and Trans. N.Z. Inst., vol. xi., p. 504). It is generally 

 found as small rhombohedral crystals, lining cavities in these rocks. 



Dendritic Iron markings are of very frequent occurrence in a,ll the harder 

 and jointed rocks, some of them being of exceeding beauty. They are 

 frequently mistaken for fossil ferns, which they very much resemble at 

 times. 



Ilmenite (Titanate of Iron). — This species includes several varieties due 

 to the isomorphous characters of titanic and ferric oxides, so that the per- 

 centage of titanic acid present varies very considerably in different speci- 

 mens. It is of very common occurrence as an accessory mineral in the 

 volcanic rocks, where it occurs as small rhombohedral crystals, affording 

 generally triangular or pentagonal sections when cut, and it enters largely 

 into the composition of many of the ironsands of New Zealand, which 

 surround so large a proportion of our coast. These ironsands are com- 

 posed of a proportion of titanic iron, ranging from 2*4 per cent, to 74-2 

 per cent, of the whole, mixed with Magnetite and Hematite in varying 

 proportions. 



It is very difficult to group these in any definite order by the amount of 

 titanic acid present, but it is noticeable that amongst those which occur on 

 the southern beaches and also in the river beds the percentage is frequently 

 high, ranging from 40 to 74 per cent, of titanic iron, and these have been 

 principally derived from the basaltic rocks of the district. 



On the other hand, the ironsands of the west coast of the South Island 

 are practically fi-ee from TiOa in many cases, while the well known Tara- 

 naki ironsand only contains from 6 to 8 per cent, of titanic iron. There are, 

 however, many ironsand deposits in Otago and Southland which contain 

 from 2 to 8 per cent, titanic iron only, so that it is impossible to assign 

 special areas over which any percentage will hold. Such, however, is not 

 the case if we seek the rocks fi-om which these' ironsands have been derived, 

 for we there find that the basaltic rocks have as a rule yielded an ironsand 

 in which the percentage of titanic u'on is over 50 ; that the granitic rocks 

 seldom yield a sand in which the percentage of titanic iron is over 8 ; and 



