REPORT ON THE PETROLOGY OF OCEANIC ISLANDS. 143 



glacier-borne erratics, lying on the sand of the shore, were so cleanly sliced by the 

 particles of magnetite and augite, that they seemed to have been chiselled. The largest 

 faces of the blocks on which the erosion has been greatest are always turned to the 

 west, the direction from which the winds are most continuous and strongest. 



From a sketch by Mr. Buchanan, representing a rock embedded in the black sand. The side towards the 

 west, with the high light on the woodcut, is being rapidly worn down by the sharp sand blown against it, which 

 has cut an irregularly fluted pattern in it. 



At the point where a landing was made, two promontories run out ; that towards 

 the west is formed of a high mountain rising up from the sea and cleft at the summit 

 into two peaks, from between which a glacier descends to the cliffs on the north-west. 

 Blocks of ice, breaking off, fall into the sea with an echoing roar. The other peninsula 

 is covered with recent lava, the scoriaceous surface of which appears not to have been 

 affected yet by erosive action. The flow extends from the base of a recent but greatly 

 denuded crater, which is worn by wave action into three fantastic peaks, whose vertical 

 walls show the successive lava-flows inclining from the centre outwards. This lava- 

 layer spreads over the whole peninsula, and forms a row of cliffs cut out by wave-action 

 along the northern part of Corinthian Bay. The glaciers covering the southern part 

 have been stopped in their descent to the sea by a conical mound of scoriae. When 

 account is taken of the slight alteration of its surface, the lava appears relatively 

 recent, and this fact, taken in conjunction with the great energy of denuding agencies 

 at Heard Island, agrees well with the view of an eruption at no distant date. 



All the rocks collected in the island are volcanic, and belong to the felspathic basalts. 

 Some are massive, others vesicular ; all may be viewed as derived from the lava-sheets 

 which have spread over the island. 



"We shall first describe those specimens collected to the south-west of the solitary 

 group of houses on the islands. Iu this place the rocks are spread out in beds, and 

 present to the naked eye all the appearance of basalt, being black and fine-grained, with 

 only olivine perceptible amongst the constituent minerals. Microscopically the rock is at 

 once classed as a felspathic basalt, the minerals of the first generation being plagioclase, 



