DISCOVERY 



93 



when visiting the island, the following were the reasons 

 for its existence. The ilows of light-coloured lava from 

 Nightingale probably extended at one time about a 

 mile farther to the north than the present northern 

 shore of Nightingale. This is evidenced by the 

 trachvtic agglomerate and trachyte seen on Middle 

 Island. Following this there was an effusion of a hard 

 compact lava from a neck which exists on the latter 

 island. The border of the neck is marked by a breccia. 

 The dykes emanating from this lava are not seen on 

 Nightingale, but some of the rocks which infest the 

 channel between the islands are probably their eroded 

 remains. The action of the sea on the mass of altered 



I trachyte between Middle and Nightingale has in the 



I course of time cut a channel through. 



Stoltenhoff Island 



It is not possible to land on this island as it rises 



of the depressed central area. The interior is broken 

 country clothed in verdure, and on account of the high 

 rim, which affords protection from the winds, would 

 be suitable for human habitation. A stream winds 

 through the interior, finaUy falling in a beautiful 

 cascade, to the beach at the north-east shore, where a 

 landing is easily made if the wind be not from the north. 

 The central cone is a mass of light frothy lava, 

 and the section from here to the sea near the water- 

 fall shows that there have been successive flows of 

 basalt and trachyte. The high cliffs to the west of the 

 landing are cut by a series of parallel dykes which are 

 an imposing feature. 



Gough Island 



Gough Island lies roughly 280 miles south of the 

 Tristan da Cunha group. It is eight mUes long 

 by three miles wide, and forms a monoclinal block 



Fig. 3.— lookout harbour, ei<eph.\nt isi,.\nd. 



sheer from the sea to about 200 ft. It is flat-topped 

 and in area about 500 yds. by 150 yds. The rock 

 of which it is composed appears to be of a trachytic 

 nature and may be the northern limit of the flows from 

 Nightingale which have already been mentioned ; it 

 may, however, be a centre of activity such as is de- 

 scribed as existing on Middle Island. 



Inaccessible Island 



Eleven miles to the north-north-west of Stolten- 

 hoff is this island, which is the most northerly 

 one of the group. It is pear-shaped in appear- 

 ance, being about three miles by two and a half 

 mUes. 



In its general features it is a basin — a great caldera 

 the south-eastern side of which has been blown out. 

 A cone rises to about 1,500 ft. towards the north-east 



with dip slopes to the west and escarpments to the 

 east. The highest point on the long ridge which runs 

 down the longer axis of the island is about 2,915 ft. 

 above sea-level. The west side of the ridge goes down 

 in a long slope to the cliffs bordering the sea. 



The escarpments on the east side are cut by three or 

 four glens ; the largest one, about half-way down the 

 coast, gives access to the interior. The most striking 

 feature lookmg up the glen is the great stock of an acid 

 intrusive rock which rises to 2,270 ft. It can best be 

 described in the words of Scott : 



" Shooting abruptly from the dell 

 Its thunder splinter'd pinnacle." 



Thick mosses and bracken grow in the glens and two 



types of tree were found. In the smaller glen, to the 



south of the main one, there is a species of Sophora,^ 



» G. H. Wilkins, M.C., F.R.G.S., NaturaUst. 



