130 



THE VOYAGE OF H.M.S. CHALLENGER. 



opposite Prince of Wales Foreland, which has a very similar structure to that of 

 certain hills at Christmas Harbour. It has an embattled appearance like a castle, 

 and is known by the name of " Cat's Ears." The rocks at the summit look like 

 ruins ; they are greyish, and contain fragments of scoriaceous lava, which 'also forms 

 a layer immediately beneath the battlemented crags. The rock contains large crystals 

 of augite, with sharp outlines, but they are always broken and rounded when observed 

 in the volcanic sand formed by the decomposing rocks. The sand has been sorted 

 out by the wind, the white grains, which are lightest, being carried away and only the 

 black particles left. These crystals and the rocks themselves clearly show the erosive 

 action of the wind, the former having lost all regularity, the latter being deeply cut 

 into on the side facing the prevailing winds. Here, as in Heard Island, where the same 

 thing can be observed in even greater perfection, the wind constantly blowing from the 

 west carries along the sand and drives it with great force against the rocks, cutting 

 and carving them in a characteristic manner. 



From this hill Mr. Buchanan, from whom we borrow these facts, could see another 

 very similar at the base of the Sugar Loaf. From a distance it resembled a druidical 

 circle, but the short time at his disposal prevented him from examining it more closely 

 or visiting the Sugar Loaf. 



Amongst the rocks we have examined, there were no specimens from " Cat's Ears," 

 nor from any other hillock of this part of the Sound, except Coronet Hill, near 



the south-western entrance. These rocks may be classed 

 as augitic trachytes, trachytic tufas, and basalts. 



The specimens of trachyte are greyish, rather com- 

 pact, with an irregular fracture ; only small crystals of 

 sanidine can be detected with the lens. Thin slices, 

 when examined, show that the rock is composed of an 

 isotropic mass containing small crystals of sanidine, 

 twinned according to the Carlsbad law, and also 

 larger individuals of the same mineral. The latter are 

 always much broken up, and exhibit undulating extinc- 

 tion (see fig. 22), as if they had been submitted to 

 section of corroded sanidine with undulating strain, a supposition which is strengthened by the linear 



extinction. ^o crossed nicols. Polarised -t IT o J 



llght - arrangement of the augite microliths. These small 



prismatic crystals extinguish at nearly 40°, and are invariably bedded with their vertical 

 axis in the plane of the preparation. Many sections of magnetite are to be seen ; these 

 are usually collected in the place occupied formerly by hornblende crystals, of which 

 scarcely a trace remains. These crystals of hornblende are always surrounded by small 

 green crystals of augite. 



Fig. 22. 



-Trachyte from Coronet Hill, 

 Royal Sound. 



