OUR BOOK SHELF. 33 
it would seem strange that rocks could be made to yield interesting 
objects—but such is the case, and as they learn that a common 
piece of limestone may be made to show its hidden structure by a 
little simple manipulation, bringing to light the beautiful skeletons 
of fossil foraminifera or the shells of mollusca, they cannot fail to 
take an interest in such a study, and wish to make themselves 
acquainted with the structure of rocks generally. 
In order to commence the study satisfactorily, a text-book is 
certainly necessary, and the one under review may with confidence 
be placed in the students’ hands ; but it must be remembered that 
in order to study these things a fair knowledge of geology and 
mineralogy is requisite. It is one thing cutting and mounting 
rock sections, and studying them quite another; still there is no 
difficulty in acquiring a good knowledge of both these branches. 
The book certainly supplies a want and should go far in creating 
a taste for petrological studies, and when this branch of microscopy 
has become more popular, our own petrologists, Sorby, Allport, 
Phillips, or our author, Mr. Rutley, may be induced to put our 
scattered literature in the form of a handbook, such as Zirkel’s or 
that of Rosenbusch in the German. 
The first four chapters are taken up with, Methods of research— 
Definition of rocks and their origin-——Disturbances of the earth’s 
crust, Structural planes, sedimentary rocks, and statigraphy— 
General character and mode of occurrence of eruptive rocks. 
Chapter V. relates to the collection and arrangement of rock 
specimens. Chapter VII. describes the microscope specially suited 
to petrological work, the author apparently giving preference to a 
monocular instrument. ‘There are many microscopists who fail to 
appreciate the exact work suited to a binocular, and a word of 
warning may be given here to those who may be using the new 
short mount objectives with the Wenham prism. Let them read 
Dr. Carpenter’s Microscope and its Revelations, p. 71, and they 
will see that our author, Mr. Rutley, is warranted in his preference. 
It should however be borne in mind that the Wenham binocular 
only reduces the angle of aperture in one direction, and therefore 
the object may be viewed without exaggeration if properly placed 
on the stage. 
Chapter VIII. treats of the preparation of rock sections, Chap. 
IX. describes their examination, and X. treats of the microscopical 
characters of the principal rock-forming minerals, which turns out 
to be one of the most interesting chapters in the book, and one 
which will be of real value to the student. 
Figs. 4 and 5 have been kindly placed at our disposal by the 
publishers, and serve to show how interesting some of these sec- 
tions may be. Fig. 4 is a magnified section of a crystal of sanidine 
occurring in rhyolite from the Rhine, it is a good polariscope 
