364 A NATURALIST IN THE PACIFIC chap. 



Riffelhorn and on one of the peaks of Monte Rosa, and fulgurites 

 have been also obtained from Mont Blanc. . . It is not always easy 

 to explain, however, isolated cases of polaric rocks where no signs 

 of fusion occur. Whilst descending into the Valle del Bove from 

 the Etna Observatory, I picked up four small volcanic bombs of 

 basic lava, of which one displayed polarity, the poles being situated 

 at the sides of the bomb. Zirkel quotes the observation of 

 Naumann on the summit of the volcano of Moryoshi in Japan. 

 Here out of a number of lava-blocks lying about only one ex- 

 hibited marked polarity, whilst the rest showed no signs of it. 



Before dealing with the polaric rocks of Vanua Levu, I will 

 refer to two localities in other parts of the group where magnetic 

 rocks have been observed. During the Wilkes' expedition in 1840, 1 

 Lieutenant Underwood observed great local attraction at Naikovu, 

 a rock 90 feet high of volcanic formation lying off the south end 

 of Nairai Island. He found a "deviation" of 13 1 points (149 

 degrees) at the top of the rock, whilst at the foot near the water 

 the needle gave correct bearings. In the Sailing Directions for the 

 Pacific Islands, published in 1900, the "deflection " at the summit 

 is said to be 87 degrees. It is stated by Mr. Eakle in his paper 

 (quoted on p. 293) on the rocks collected by the recent Agassiz 

 expedition that this rock is composed of an augite-andesite. ... I 

 have learned from Mr. Alex. Barrack that there are some highly 

 magnetic rocks on the west coast of Viti Levu in the vicinity of 

 Likuri Harbour in the Nandronga district. It is said that speci- 

 mens sent down to the colonies were found to contain 95 per cent, 

 of magnetite. 



It is very probable that the results obtained by me for Vanua 

 Levu can be generally applied to the other large islands of the 

 group. The observations were made during my various geological 

 journeys and deal only with certain aspects of this interesting 

 subject. 



The first feature in this connection is the frequency with which 

 simple magnetism is displayed by the acid as well as basic volcanic 

 rocks of this island. About 95 per cent, of the volcanic rocks 

 collected attract both ends of the needle. 2 This property of 

 volcanic rocks is well known, and is to be attributed to the mag- 



1 Wilkes' Narrative of the U.S. Exploring Expedition, in., 185. 



2 Of the tuffs and clays, almost all submarine and often containing tests of 

 foraminifera and sometimes molluscan shells, about 90 per cent, exhibit simple 

 magnetism in a slight degree, but out of nearly 100 specimens tested none show 

 polarity. 



