564 Reviews—Rocks of Cape Colville, New Zealand. 
but no doubt contains enough for the student’s requirements. To say 
that it is the best work in the English language on this subject is 
unnecessary ; 1t compares very favourably with any of the French or 
German manuals in current use. It will not obviate the use of the 
larger treatises, such as Rosenbusch-Wilfing, but will serve as an 
admirable introduction to them, and should find a place among the 
working manuals of every student of petrology. 
Very few inaccuracies have come to our notice in reading the book. 
We may point out, however, that the Canada balsam on which rock 
slides are mounted has by no means a constant refractive index of 
1:539; it varies somewhat, and is often 1°542 to 1°544, and this is of 
some importance in determining felspars, nepheline, ete. The student 
should be warned to test it for himself in slides containing quartz. 
The use of the selenite plate in determining the sign of axes and 
bisectrices of biaxial crystals should be given; it is much to be 
preferred to a mica plate, and is one of the most useful accessories 
to a petrological microscope. Some description of the method of 
measuring optic axial angles should certainly be provided; nowadays 
by means of a Schwartzmann’s scale this is a very simple operation. 
Professor Iddings makes the very useful suggestion that the capital 
letters X, Y, and Z should be used to designate the three principal 
axes of the triaxial ellipsoid. We hope it will be generally adopted, 
as it will save a great deal of trouble in correcting printers’ proofs. 
In the tables at the end of the book the minerals are classed as 
isotropic, uniaxial, and biaxial, and given in groups arranged according 
to their refractive indices, a method which has many advantages to 
recommend it. The excellent coloured plate of interference colours, 
originally prepared by Lévy and Lacroix, is reproduced and will be 
greatly appreciated both by teachers and students. \ 
II.—Rocxs oF tHe Cape Cotvitte Pentnsuza, New Zeatanp. By 
Professor Sotzas, with introduction and descriptive notes by 
ALEXANDER McKay, F.G.S. 
HE Cape Colville Peninsula is part of the well-known Hauraki 
mining district, the source of large quantities of gold within the 
last forty years. It contains a great variety of igneous rocks, many 
of which are in advanced stages of decomposition and solfataric 
alteration. Many names had been applied to them by the miners, 
and it seemed necessary to get an authoritative classification ; for that 
purpose about four hundred specimens were sent to Professor Sollas, 
who has written brief descriptions of them. A general account of the 
region is provided by Mr. McKay, who has apparently acted as editor 
of the volume. It is the first effort to treat of the petrography of 
this area asa whole. The book is illustrated by a large number of 
whole-page photomicrographs, which, while they are not all of equal 
excellence, often give a very clear idea of the structure of the rocks 
which are under description. 
Volcanic action has gone on in this district in Paleozoic (Devonian 
and Carboniferous) and in Tertiary times. The igneous rocks are 
principally andesites of various types, dacites, rhyolites, and obsidians, 
