REPORT ON THE PETROLOGY OF OCEANIC ISLANDS. 105 



lies between the parallels of 46° 48' and 46° 56' S. latitude, and the meridians of 

 37° 35' and 37° 54' E. longitude. 



The island seems to be entirely volcanic. The highest land is in the centre, and 

 irregular slopes lead down to the sea on all sides. These slopes are of very moderate 

 inclinations, and are broken in numerous places by shallow valleys bounded by cliffs 

 where the more ancient flows of lava have suffered denudation. These valleys are now 

 occupied by more recent lava-flows, which still retain their rough pinnacled upper 

 surface. Further, all over the slopes and summits are scattered irregularly numerous 

 small cones, formed mostly of conspicuously red scoriae. The lava presents in many 

 places in the cliffs a columnar structure. Some sand gathered on the shores of a small 

 fresh-water lake near the sea was full of augite and olivine crystals. 1 



In attempting to reach the actual upper limit of vegetation, Mr. Buchanan made 

 some geological observations, and collected some specimens of the rocks which will be 

 hereafter described. The ascent was up the bed of a small stream, which lay at the 

 verge of one of the modern lava-flows, where it abutted on a low cliff exposing a more 

 ancient flow in section. The more recent flow had a very gradual inclination of not 

 more than 8°. The stream was found to flow over an apparently very recent stream of 

 black cellular lava, the ripples and eddies in which were still perfectly fresh, except in 

 the very centre, where they had suffered some slight abrasion. This lava was basaltic 

 and contained much olivine. Close by the bed of the stream rose several red conical 

 hills. One of these, the highest within reach, consisted of a heap of loose scoriae dis- 

 posed in layers, dipping away on all sides at a regular and very steep angle. Few of 

 these pieces of scoriae were more than six inches in diameter. At the top was a 

 perfectly conical pit, and slightly below the summit, on the north side, were three 

 smaller and similar pits. The scoriae of which the hill is made up consisted of a highly 

 cellular red ground-mass, with indications of augite, without, however, any perfect 

 crystals being discernible. Besides the red scoriae, there were some of a chocolate- 

 brown colour, with frothy exterior and compact kernel, resembling almond-shaped 

 volcanic bombs. Besides this hill, there were five or six others precisely similar in 

 appearance and rising out of the same valley. From the top of the hills this valley or 

 depression could be seen to be bounded, towards the interior, by a semi-circular cliff of 

 rocks, in some parts columnar, and open to the sea. Above this cliff rose the snow- 

 covered cones and peaks of the interior, which seemed to be similarly formed to those 

 of the lower ground. On leaving the stream-bed and returning to the eastward over 

 the spur of the mountain, the cliff was found to consist of a light-grey compact doleritic 

 rock. 2 



All the rocks which were collected at Marion Island by Mr. Buchanan, and which 



1 Moseley, Notes of a Naturalist, p. 164. 



2 Narr. Cball. Exp., vol. i. pp. 300, 301. 



(PHYS. CHEM. CHALL. EXP. — PART VII.— 1889.) 14 



