xxvi MAGNETIC ROCKS 



3 r >9 



Though it displays bare rock-faces, the actual peak has a soil -cap 



at least 18 inches deep and supports small trees and shrubs. 



Notwithstanding this, I found when standing on the peak that 



my compass was very noticeably affected, the pull being to the 



eastward, whilst the amount of deviation increased from u° to [6 



when changing from the sitting to the standing position. Specimens 



of blocks from the agglomerate forming a rock-face 10 feet below 



the summit possessed polaric powers of 12° and 5 . Others of the 



same rock exposed in a cliff-face 450 feet below had a weak 



repellent power of only 4 . . . As in the case of Mariko, the top of 



Thambeyu (2,700 feet) is vegetated ; and beneath the smaller trees 



blocks of polaric rocks lie on the surface. One of these, a 



pyroxene-andesite (sp. gr. 272), from which I obtained a specimen, 



has a polaric power of 38°. In another case, that of an amyg- 



daloidal rock of the same character, the repellent power is 14°. 



I might mention seveial other polaric peaks, but it will be 

 sufficient to refer to one or two other localities. In the mountainous 

 basaltic district around Solevu Bay the peaks are usually polaric. 

 Specimens from the top of Uli-i-matua, 1,100 feet, have a repellent 

 power of 1 5 . The three-peaked hill of Koro-tolu-tolu appears to 

 be in the mass of polaric basalt from the foot to the summit, having 

 a repellent power varying from 4 to 30°, the most active specimens 

 being obtained from the lower slopes, which, however, are scantily 

 covered with trees. Samples of the grey basalt from Koro-i-rea 

 show polaric powers of 3 to 7'. 



As examples of the numerous lesser hills with bare rocky 

 polaric summits I will first take Bare-poll Hill facing Soni-soni 

 Island. This hill is only about 150 feet above the sea, its top 

 being formed by two large masses of a basic andesite lava with 

 a glassy groundmass, incrusted with agglomerate, the whole 

 representing a volcanic " neck." A specimen of the rock masses 

 has a repellent force of 22 . Another instance is afforded by 

 Vatui, a hill 450 feet in height situated south of Mount Sesaleka. 

 Its summit is capped by a naked mass of tuff-agglomerate 

 pierced by a dyke 18 inches thick of an olivine-basalt, with a 

 specific gravity of 2^90 and a polaric power of io°. 



A somewhat suggestive example is afforded by the hill of Na 

 Suva-suva, 1,110 feet high, which overlooks Naindi Harbour to the 

 east of Savu-savu Bay. It is only occupied by trees in its upper 

 part, and a specimen of the olivine-basalt, of which the hill is 

 composed, that was obtained from the wooded summit, shows no 

 polarity ; whilst another from the slopes, two- thirds of the way up, 



13 B 



