1887. ] MICROSCOPICAL JOURNAL. 59 
NOTICES OF BOOKS. 
* Modern Petrography -—An Account of the Application of the Microscope to the Study 
of Geology. By G. H. Williams. D. C. Heath & Co., Boston, 1886. (pp. 35). 
Paper covers. 
This little work, as its title suggests, is not a manual of the science, or, in any sense, 
a guide to be used in work, but it is rather an essay addressed to teachers more scien- 
tific than a popular magazine article can be, and not too profound for those of our 
teachers who are not most deeply learned in the science. The purpose of the book is 
to sketch the science of Petrography in such a way as to present a clear view of it. It 
is the study of rock-sections, or, more exactly, it aims to show the principle of interpre- 
tation of rock-sections for geological purposes. In doing this, it follows, in historical 
summary, the growth of the science as a special branch of geological study from 1862, 
when Zirkel first began, in Vienna, to study rock-sections, and active study was com- 
menced in various places, and the detection of the minerals constituting a rock, by 
microscopical character, became a science and an important division of lithology. 
At first etrography was only of assistance to mineralogy as furnishing additional 
diagnostic tests of mineral species. But ‘as time goes on petrography will not yield her 
best services to the mineralogist, but to the geologist, by placing at his disposal a new 
and potent means for successfully dealing with many of the problems presented in the 
earth’s crust.’ 
For historical geology it is for unfossilferous rocks what palzeontology is for fossili- 
ferous, or is rapidly becoming so understood as to be so used. The economic appli- 
cation of the microscope in geology is seen in the study of building-stones, whereby 
their durability can be predicted with far increased reliability. 
In addition to the excellent historical sketch and the statement of what petrography 
is to-day and will be, there is a bibliography and four pages upon (1) the method of 
preparing rock-sections, (2) note upon Petrographical Microscope, (3) names of Arep- 
arateurs from whom slides may be purchased. 
The book is a thoroughly satisfactory little book, admirably presenting the subject. 
It is one of a series of Monographs on Education, published by D. C. Heath; others 
published are on Latin in Preparatory Course, Mathematical Teaching and its Modern 
Methods, and How to Teach Reading, and what to Read in the Schools, and others 
are promised. 
The Journal of the Royal Microscopical Society, February number, has just reached 
us, and we find that it contains a very admirable paper, by Prof. Abbe, upon the new 
optical glass, a full account of which we shall hope to present at some future time. 
The same number contains an article by Dr. A. C. Stokes upon the Infusoria, with a 
beautifully executed plate, and in addition the usual summaries of current researches 
in biological science. 
An Elementary Course in Practical Zoology. By B. P. Colton. D.C. Heath & Co., 
Boston, 1886. (pp. 185). 
In this work its author has succeeded well in filling a gap in the series of American 
science text-books by preparing for high-school classes a book which is a great step 
in advance of anything hitherto in the field. It would be more proper to call the work 
a natural history of animals, perhaps, than a zoGdlogical work; but laying aside any 
bickering over the name, the thing itself is a good one. The work is a practical guide 
of the sort so much in vogue at the present time, and following the original suggestion 
of Huxley & Martin’s ‘ Biology,’ directing the young pupil’s steps in observations upon 
the coarser anatomy of a great variety of animals. Among those treated may be men- 
tioned the grasshopper, cricket, bumble-bee (which is properly called humble-bee), 
butterfly, house-fly, squash-bug, spider, crayfish, cyclops, earthworm, fresh-water mus- 
sel, snail, amoeba-fish, frog, snake, turtle, pigeon, rabbit, starfish, Hydra, and sponge. 
In all thirty-two forths are treated, and the pupil works them through, and can study 
out for himself, without greater skill than a young boy or girl should possess, all the 
features which are pointed out. It is the purpose of the work to set tasks for the ele- 
mentary student, the performance of which is within his power. It is a good thing to 
set young pupils at work upon these anatomical studies, which will require close and 
discriminative observation. Unlike many elementary works and some manuals, the 
work is very free from misstatements of fact, the author having had the benefit of 
thoroughly testing his descriptions and their thorough revision by several able zodlo- 
