6 ME. J. S. GABDINER ON THE GEOLOGY OE EOTFMA. [Feb. 1898, 



in Itomotu at the western end, but the level of the former seems 

 little below that of high tide. 



The outlying islands on the reef all seem to be of the same 

 structure, a rough, reddish ash-rock, mixed with chips of harder, 

 black rocks, which on examination appear to be lava, some other 

 volcanic agglomerate, or of basaltic nature; they are, however, 

 very rarely crystalline. Sometimes these foreign rocks occur in 

 large masses, and indeed the southern end of Afaga is formed entirely 

 of a basaltic rock. The two islands of Howa, opposite Oinafa, were 

 obviously once joined, but the ash-rock has been washed away 

 between them, leaving a channel, now covered by 2 to 3 feet of water. 

 In it, however, are many blocks of hard black rock from the dis- 

 integration of the ash-rock. Two-thirds of the way from Howa to 

 Afaga lie two rocks about 20 yards outside the breaking edge of the 

 reef, apparently of a basaltic nature. Afaga, as before mentioned, 

 has its southern end of a compact lava or basalt, together with many 

 rocks lying in the reef off its southern end. Towards the sea it is 

 precipitous, but the section fails to show any sharp distinction between 

 it and the ash-rock. The latter has its strata dipping slightly at an 

 angle of 2° or 3° to the N"., while generally, if the strata show at ally 

 they are perfectly horizontal. Between Afaga and the shore rises 

 a small ash-rock island, Husia, with precipitous walls about 40 feet 

 high. It has been considerably washed away within the memory 

 of many Eotiimans, a strong current with a deep channel (9 feet) 

 running between it and the shore. 



Sol Kopi is about 350 feet high, with precipices, often over- 

 hanging the sea to the outside from 50 to 200 feet high, while Sol 

 Onau has a similar structure. Towards the sea, indeed, all these 

 islands of volcanic ash end precipitously, but under them is always a 

 narrow fringing-reef 10 to 20 yards broad. Some, too, show traces 

 of extensive landslips. 



The Western End. 



The part thus designated is very sharply separated from the 

 beach-sand flat at the isthmus by steep cliffs of 70 to 100 feet, 

 surrounding the base of Kugoi, while the same hill continues to the 

 south by a ridge into Kiliga, but to the north has a sharp drop 

 into a valley from which Sororoa rises to the height of about 850 

 feet. 



Kugoi and Kiliga are bounded on all sides by precipitous cliffs, 

 150 to 250 feet high, but on the west have been to some extent 

 banked up by a flow of lava from a crater halfway up Sororoa, the 

 greater part, however, of which mountain is of ash-rock, as also is 

 the hill of Mea to the west. 



Somewhat westward of Mea rises a small, perfectly conical- 

 shaped hill, called Mafiri. It is nearly 200 feet above the general 

 level and about 350 feet above the sea. It is covered everywhere 

 with big rough blocks of black, extremely vesicular, but heavy lava, 

 in which are many small caves, 15 to 25 feet deep. On the top is a 



