A Contribution to the Petrology of Kerguelen. 211 



Royal Soimd. — Two specimens corae from this place. One is 

 a tine-grained dark coloured rock, breaking with a sub-concoidal 

 fracture. The slices prepared from it show an entirely opaque 

 base, in which crystals of hornblende, augite and apatite can be 

 seen. No traces of felspar can be detected. In many cases the 

 interior of a crystal has been entirely replaced by magnetite, 

 while a bordering zone of translucent material showing weak 

 polarisation tints has been formed round the altered crystal. 

 The other specimen is a small rounded pebble of grey colour and 

 fine-grained texture. There are certain markings on the external 

 surface which simulate the appearance of a fossil, but on exami- 

 nation they are seen to be due to zeolitic matter. Under the 

 microscope the rock is found to be made up of grains of augite 

 pseudomorphic after hornblende, wedged in between lathshaped 

 interlacing felspars twinned according to the Carlsbad law. 

 These felspars present the typical " trachyte " structure ; they 

 have a certain linear disposition and show a tendency to flow 

 structure around the phenocrysts of felspar and augite, which 

 they enclose. The character of the felspars points to sanidine, 

 but the amount of alteration which the rock has undergone 

 makes exact determination difficult. I am inclined to class the 

 rock as an augitic trachyte, specimens of which are described from 

 other parts of Kerguelen Island. 



" Cafs Ears." — The rocks from this locality are the most 

 important collected by Mr. Hall. Though a description of the 

 hill at the south-west entrance to Royal Sound, known as " Cat's 

 Ears," is given in the Challenger volume, no rocks from the hill 

 were submitted to Professor Renard for examination. Seven 

 specimens — suitable for slicing — were brought back by Mr. Hall, 

 and form an interesting series. 



1. A somewhat decomposed vesicular lava in which triclinic 

 felspar, augite, magnetite and altered olivine occur in a glassy 

 base. 



2. A decomposed rock in which the minerals which can be 

 determined with certainty are plagioclase felspar — in minute 

 lath-shaped crystals — augite and magnetite. There is a con- 

 siderable amount of glass present, and in it are numerous colour- 

 less acicular crystals of what is probably apatite. 



