90 A NATURALIST IN THE PACIFIC chap, 



magnetite than in the grey basalts. There seems to be no inter- 

 stitial glass ; and the olivine when not fresh is usually serpent- 

 inised but occasionally haematised. 



The dark basalts of Ulu-i-ndali when they occur on its upper 

 slopes become ophitic. A specimen lying beside me has a specific 

 gravity of 2*9 1. Allowing for the structural differences, it appears 

 as an ophitic surface variety of the deeper seated grey basalts. A 

 description of it is given under genus 12 on page 256, of which it 

 forms the type. 



From the data above given, the hill of Ulu-i-ndali is to be 

 regarded as the basal portion of a submarine volcano still retaining 

 part of its ash-coverings. The grey doleritic basalts probably 

 represent the core and the dark fine-grained basalts represent the 

 flows of this ancient vent. 



The Kumbulau Peninsula. — South-east of Ulu-i-ndali 

 stretches a remarkable " talasinga " district which for convenience 

 I will call the peninsula of Kumbulau. Its south or seaward 

 border is broken and hilly, and presents an irregular line of hills 

 300 to 470 feet in height, extending from Kumbulau Point to 

 Soni-soni Island, which is almost connected with the coast. The 

 rest of the peninsula is a low-lying and often marshy plain, which, 

 though elevated in some places 20 to 25 feet above the sea, is 

 usually much lower. On the north-east side of the isthmus is the 

 narrow Nandi inlet, bordered by low mangrove-belts, which repre- 

 sents the broad channel that in a very recent: period of the island's 

 history cut through the present neck of the peninsula between the 

 head of the Nandi inlet and Ravi-ravi. 



Stratified and often steeply inclined tuff-sandstones and clays, 

 more or less basic and palagonitic in character, form together 

 with basaltic agglomerates the prevailing rocks of the peninsula, 

 whether in the hilly portion or in the plains. They belong to the 

 basic tuffs of mixed composition described on page 330 ; and though 

 the agency of eruptions can be recognised in their components 

 they are also the products of marine erosion. 



Some of the hills represent volcanic " necks " ; whilst the low 

 narrow promontory between Kiombo and Soni-soni Island has 

 been formed by an old basaltic flow. 



I will begin the description of this peninsula with the eastern 

 extremity north of Kumbulau Point, the interior of which is cut 

 up into ridgy hills 300 to 350 feet in height. On its eastern coast 

 are exposed volcanic agglomerates, composed of large blocks, 

 which from their dimensions given below would weigh between 



