233 



■^qtiartz grains are also present. For remarks on the probable 

 chemical composition of this rock see page 235. 



At Horn's camp there occurs a rather coarse-grained 

 rock with idiomorphic felspar tabulae, up to 3 or 4 mm. in 

 length ; the matrix is a fibrous cleavable dark-green ferro- 

 magnesian mineral. Tn texture the rock appears to be 

 intermediate between the ophitic and gabbroid types. Miner- 

 alogically it is exceedingly altered ; no mineral appears to be 

 primary. The felspar is changed to colourless finely-granular 

 epidote, with meionite and a little quartz, together with a 

 very little clear indeterminable secondary felspar (albite?). 

 The epidote grains are in optical parallelism, extinguishing 

 simultaneously over a considerable area. They are slightly 

 pleochroic. The pyroxene has become actinolite of a pale- 

 green colour, which does not always lie parallel to the verti- 

 cal axis of the original pyroxene grain. The border of the 

 actinolitic areas is somewhat darker in tint, being composed 

 of finely granular chlorite. Traversing the rock is a vein 

 filled with dark-green matter. Microscopically this is ex- 

 cessively fine-grained, appearing to consist of a pale-green 

 amphibole mixed with epidote and quartz. It is far too fine- 

 grained, however, for certain determination. 



I would place among the gabbro-diabases, also, a rock 

 labelled "12 miles east of Blinman." It is similar in a general 

 way to the rock first described in this group, but the grano- 

 phyric intergrowths of qua,rtz and felspar are entirely absent. 

 The felspar is largely changed to saussurite and the pyrox- 

 ene to fibrous or compact hornblende, with the formation of 

 a little secondary magnetite. 



These paramorphs are often separated from the saus- 

 surite by narrow, bands of scapolite ( ?), whose fibres or 

 cleavages stand perpendicular to the limiting surfaces. 



Chemical Notes. 

 This paper as originally presented contained no analyses, 

 but on the request of Mr. Howchin and Mr. Mawson I have 

 made the analyses given below. It is hoped that the short- 

 ness of the time available between the reading of the paper 

 and its publication, during which I had also my official duties 

 to perform, will be sufficient excuse for the lack of complete- 

 ness of the analyses. The rocks chosen were the olivine-dia- 

 base from the west side of Blinman Mine (A), which is de- 

 scribed on pages 228-9 and shown on pi. xv., fig. 2, and (B) a 

 gabbro-diabase, labelled "one mile west of Blinman," but 

 very similar to the saussuritic gabbro-diabase from 12 miles 

 east of Blinman last described. 



