146 



Prof. T. G. Bonney. 



[June 15,. 



crossed the Hag'gier Mountains to the southern coast, and returned 

 again to Hadibu, on the north side, by a route lying further to the 

 west. During this journey, in addition to extensive botanical and 

 zoological collections, Professor Balfour obtained about 500 rock 

 specimens illustrative of the geology of a considerable portion of the 

 island. These were sent to the author for examination. A consider- 

 able number of them, as was to be expected, were more or less 

 weathered, and so were*not in a very favourable condition for precise 

 description ; but about eighty of the best preserved specimens have 

 been examined microscopically ; from the study of which, and of the 

 remainder the following sketch of the geology of the island may be 

 given. 



The north-west, inland from Gollonsir Bay, consists of a plateau of 

 limestone resting unconformably upon a group of highly crystalline 

 gneisses, associated with diorites, which correspond in general cha- 

 racter with the Hebridean series of north-west Scotland. The latter 

 group is frequently exposed in the beds of the valleys, the uplands on 

 either side being formed of the limestone. The elevated district 

 traversed between Gollonsir and Kuhmeh Bays is similarly consti- 

 tuted, but it is probable that some true granite also exists among the 

 older series ; the limestone extends all along the coast of the latter 

 bay, having its usual foundation, and there is evidence that felsites 

 occur somewhere in this district, most probably inland from the 

 eastern shore. In this part are basalt dykes, which cut the limestone 

 as well as the older rocks. 



Near the coast of Hadibu Bay, west of that town, we have limestone, 

 conglomeratic at base, resting on an indurated shale or argillite, together 

 probably with an intrusive rock approaching kersantite in character. 

 The argillite is also found inland beneath the limestone, south-east of 

 Hadibu. The Haggier mountains, a fine chain forming a sort of back- 

 bone to the island, consist of felspathic granites, varying from coarse 

 to fine, the former containing little besides quartz and felspar (the 

 variety pegmatite), through which have broken minette, basalt, and 

 felsite ; the limestone may be traced some distance up their flanks. 

 East of the Haggier, the granite rock continues, but quartz-felsites, 

 and even rhyolites, appear to become more common, and an epidotic 

 quartzite gives an indication of the occurrence of the metamorphic 

 group. Granite and felsites form the inland district traversed by the 

 river which passes Maaber, as well as the eastern half of the Haggier 

 mountains. 



The district in the neighbourhood of the coast between this and the 

 next river to the east, consists of granite cut by felsites, rhyolites, and 

 diorites, or dolerites. Possibly the gneissic series reappears here. 

 Further east yet we obtain clearer indications of the latter, overlain as 

 before by an extensive capping of limestone. Thus, the main axis of 



