32 
NATURE 
[ NOVEMBER 12, 1903 
formation, It is possible, as Mr. Guppy explains, that 
the island even now is slowly rising. 
A considerable part of the volume is devoted to the 
petrology of Vanua Levu. Plutonic rocks occur, 
though on a smaller scale than in Viti Levu. These 
are norites (hypersthene-gabbros) and a few diorites 
(without augite). The rest of the igneous rocks are 
volcanic, consisting of olivine-basalts, augite-andesites 
with and without hy persthene, and acid andesites pass- 
ing into dacites, in which sometimes the ground-mass 
exhibits a felsitic structure. Mr. Guppy’s careful study 
of these is a valuable addition to knowledge, though 
the voleanoes of Vanua Levu have not yielded any rock 
of exceptional interest. But we think he lays too 
much stress on varietal details, and that his ‘ orders, 
suborders, genera and subgenera ”’ have often no more 
than a specific value, end that he attaches too much 
classificatory importance to the presence or absence of 
Fic. 1.—Mbenutha. 
phenocrysts (to follow him in using this modern petro- 
logical slang-word). They have an important relation 
to the history of the rock, but not very much to its 
chemical composition, and thus to its position among 
the magmatic products of the earth. A porphyritic 
rock is a ‘‘ rock with a past,’? which a non-porphyritic 
rock either is free from, or successfully conceals. Mr. 
Guppy has ‘‘ gone one better’’ than most modern 
terminologists. Throughout his descriptions he talks 
of felspar-lathes, meaning thereby the microliths, 
generally called lath-like. In English a lath means a 
long blade-like strip of wood, used, for instance, in 
ceilings, and not inaptly designating microliths of fel- 
spar, especially plagioclastic, while a lathe is a machine 
for turning wood, &c. We doubt also whether the 
formulae which Mr. Guppy employs to summarise the 
characters of his rocks will be any real help to the 
NO. 1776, VOL. 69] 
memory, for they introduce the perplexities of gibberish 
without attaining the simplicity of mathematical 
symbols. Palagonite is very abundant at Vanua Levu, 
‘‘from the sea border to the mountain top.’’ Mr. 
Guppy discusses at some length the origin of this sub- 
stance, coming to the conclusion that it is usually 
associated with basalt of an ophitic or semi-ophitic 
habit, is likely to be formed extensively on the surface 
of submarine basaltic flows, and is a vitreous condition 
of magma that remains fluid after the mass of the rock 
has solidified. An exceptionally hydrous state of a 
basic magma would probably be very favourable to the 
formation of palagonite, but whether the proposed 
petrological relation will hold generally good is 
perhaps doubtful. 
But in expressing dissent on a few points, which 
are really of minor importance, we gratefully acknow- 
ledge that Mr. Guppy has accomplished a_ very 
Agglomerates on tuffs, &c., containing Foraminitera and Pteropods, now r1oo feet above sea-level. 
laborious and often difficult, if not dangerous, task, 
and that his book, when completed by accounts of his 
botanical and other work, will be a most valuable 
addition to our knowledge of this group of islands and 
to the past geological history of a large area in the 
Pacific Ocean. T. G. BONNEY. 
ELECTRIC CONVECTION.* 
Ape paper closes in a satisfactory manner an im- 
portant controversy. It follows from the views 
of Faraday and Maxwell that a charge of electricity 
when in motion produces a magnetic field in its 
neighbourhood. It is this effect on which the modern 
1 “ Recherches Contradictoires sur l’Effet magne'ique de la Convection 
électrique.” Par MM. Harold Pender et Victor Crémieu. (/ournal de 
Physique, September, 1903.) 
ee 
