570 Reviews—F. P. Mennell’s Petrology. 
of his residence in the Thames Valley in prehistoric times, we are also 
furnished with a long list of the animals (thirty-five are recorded) 
which he saw and hunted (pp. 76-7), most of which are now extinct 
or are no longer living in Britain, but which were then indigenous to 
the London district. In Chapter 1X the Holocene or Recent deposits 
are described, and much interesting information is given as to the 
wild Mammalia which had their home around British London and in 
Roman and later times. Some twenty-four species are recorded on 
pp. 99-100. 
Water supply is not neglected (see Chapter X), and some yery 
interesting records are given of old sources of supply. The Metro- 
politan Water Board have now to provide for a population of nearly 
seven millions of inhabitants at the rate of 30 gallons, or a little 
more, per head daily, the daily amount of water required being about 
225 millions of gallons (p. 115). 
The author in his conclusion reminds us that ‘‘ the present diversified 
features are the result of a great series of changes of earth-movements, 
erosion, and deposition, accompanied by varying conditions of scene, 
climate, and life; and how the aspect of the country has been modified 
in later times by the agency of Man. . . . We have further shown 
how the geological structure has influenced the water supply, and 
how the different strata have yielded materials of economic value, 
conducive to the well-being of the community”’ (p. 132). 
We congratulate the author (Mr. Horace B. Woodward), who has 
followed in the steps of his predecessor (Mr. W. Whitaker) and 
' has produced an excellent and useful memoir upon the area of the 
greatest and most populous city on the globe. The maps specially 
deserve commendation, and the price of the maps and the memoir are 
both extremely moderate. 
III.—Awn Inrropucrion to Prrrotoey. By F. P. Mennentt, F.G.S8. 
8vo. London: Gerrards, Ltd. 
fYXHIS little volume of some 200 pages presents an attractive 
appearance, and in its internal arrangement gives evidence 
of much thought and an acute appreciation of some of the difficulties 
which beset an elementary student of petrology. The plan of the 
work is distinctly good, but unfortunately the chapters do not fulfil 
the promise of their headings. The first half of the book, which 
deals with general principles and rock minerals, is the weaker portion, 
and it is evident that the second half, which treats of rocks and rock 
structures, was that part of the work with which the author was 
most at his ease. 
It is to be regretted that the earlier portion does not fulfil the 
purpose that the author intended for it; had it done so, the volume 
as a whole would have formed a self-contained and most useful guide 
to the microscopical study of rock-forming minerals and rocks. 
In reading the earlier chapters it is impossible to pass without 
comment such statements as the following, which, if not quite 
incorrect, must at any rate lead to much confusion. On p. 25 he 
says: ‘‘ Every mineral refracts light to a certain extent, that is to say, 
