REVIEWS 95 
nesium, iron, manganese, and zinc groups. The greatest need for 
improvement in the earlier editions was in the scope of the determinative 
tables, which have been expanded with considerable success. 
A. D. B. 
Microscopical Determination of the Opaque Numerals. By JOSEPH 
Murpocu. Pp. vi+165, figs. 9 (index of cuts). 
A determinative key for use in connection with the metallographic 
microscope is provided in this book. As the first work of its kind the 
book has already found wide use. The fundamental basis of classifica- 
tion is color (of the polished surface), followed by hardness and micro- 
chemical tests. A number of so-called minerals are thought by the 
author to represent mixtures rather than well-defined compounds, but 
these, with a number of unknown minerals discovered in connection with 
the studies on which the key is based, are given place in the key. 
The book is remarkably satisfactory for a first attempt in the field, 
and has already made possible the use of the metallographic microscope 
in colleges where no research work can be undertaken. 
Aa: Be 
Geologic Map of West Virginia. By I. C. WuitTeE, R. V. HENNEN, 
D. B. REGER, and R. C. Tucker. Morgantown, W.Va.: 
_ State Geological Survey, 1917. 
A revised map of the state, showing coal, oil, gas, iron ore, and lime- 
stone areas, on the scale of eight miles to the inch. A list of coal mines 
by counties, printed on the sheet, includes those in operation up to July, 
1917, except for some that are doubtless only temporary producers. The 
geology of areas other than those mentioned is not shown, nor is there 
any stratigraphic division of the limestone areas. 
AG DB: 
Economic Geology, 4th edition. By HerinricH Rigs. London: 
Wiley & Sons, 1916. Pp. xvili+856, figs. 291, pls. LX XV. 
In the fourth edition this well-known work has been considerably 
expanded and materially improved, both in the treatment of topics and 
in the descriptions of deposits. Many illuminating figures and diagrams 
have been added. Among the more noteworthy changes are the expan- 
sion of the chapter on petroleum and the chapter on ore deposits, and the 
addition of descriptions of many of the important Canadian deposits. 
