Speight. — On home Bocks from Campbell Island. 553 



such occurs, yet it seems highly unlikely that any payable 

 deposit exists. 



During the French expedition to the island in 1874 for 

 the purpose of observing the transit of Venus, a careful study 

 was made by members of the scientific staff, and no traces 

 of any metallic ores were found. Perhaps the presence of 

 iron-pyrites in small amount in one of the specimens has 

 encouraged the hope that gold may occur. As I have not 

 visited Campbell Island I have no personal knowledge of its 

 geological structure ; but an excellent account of it is given in 

 Filhol's " Mission de l'lle Campbell," which I have found of 

 much assistance. I have no knowledge of the field relations 

 of the rocks under consideration. 



No. 1. 



This is a greyish-white rock, so much weathered that an 

 accurate determination is difficult. The specific gravity is 

 2-56. To the eye it appears holocrystalline, with crystals of 

 felspar plainly visible ; some of these are 5 mm. in length. A 

 brassy yellow mineral is also present, but I could not deter- 

 mine it for certain ; it has, however, all the appearance of 

 iron-pyrites. On treating the rock with acid there is a 

 marked effervescence in every part, owing to the presence of 

 calcite. The soft character of the rock makes it difficult to 

 treat microscopically, but thin sections show plainly that it 

 is holocrystalline, and composed principally of much-decom- 

 posed felspar. A large proportion of this is so weathered 

 that it could not be determined accurately, but the lamellar 

 twinning shows that some is certainly plagioclase. Whether 

 it is all plagioclase I cannot say, but the occurrence of calcite 

 in large quantity points to the presence of a basic felspar. It 

 is possible that this may be partly due to infiltration from the 

 limestone deposits which occur on the island. The calcite 

 permeates the whole rock, and sometimes occurs in masses 

 1 cm. in length. There is also an amount of amorphous black 

 matter which is no doubt due to the decomposition of the 

 original ferro-magnesian mineral. I detected none in the 

 slides, but the examination of crushed fragments showed 

 small grains of a brown mineral which is perhaps horn- 

 blende. 



The foregoing description shows the rock to be either a 

 weathered syenite or diorite, most probably the latter. In the 

 report of the Colonial Laboratory for the year 1903, page 10, 

 there is the analysis of a Campbell Island diorite ; but the 

 percentage of CaO is too low for the rock under consideration, 

 and the absence of C0. 2 is a further proof that the two rocks 

 are different. This may be due to the introduction of a vary- 



